It is a tradition in the family that Ernest had a company making jam, which went bankrupt because he put too much top-quality fruit into the recipe. I therefore tried to track down his company, because we have in the family no documentation beyond a rather good handwritten recipe for strawberry jam.
I had two things to go on – the places where he lived, and the knowledge that he certainly did work in the jam-making industry for quite a time.
The confidence that he worked in the industry comes from his publications. As you can see elsewhere on this site he used his interest in microscopy of jam and in particular the hunt for adulterants as a major topic for his photography. He exhibited microphotographs of jam and jam adulterants on several occasions with the Royal Photographic Society. This was going on mainly in the period 1913 to 1917. He also gave a lecture at the Royal Society of Arts on the 10th of February 1913 on the same subject. He may have been professionally involved in jam making as late as 1926, because on September 20th of that year The Times newspaper printed a letter from him headed “What is jam?”. Here it is:
For a number of years the Sale of Food and Drugs Act of 1875 acted as an effective deterrent to the sophistication of jams, but gradually methods of circumventing the statute were perfected. Of these the first was to filter the adulterants, whilst the “declaration” defence in case of detection and prosecution formed the second line.
Let us consider these two topics separately. Twenty years ago apples reduced to a pulp, from which the pips and cores were removed by machine sieves, were the chief adulterants; green gooseberries, a food rich in pectin, were used when available in the more expensive jams, such as raspberry and strawberry, and lemon pulp or juice found a place in apricot jam. These crude adulterants were, however, readily detected by a microscopic examination, so jam-makers resorted to filter bags, such as, on a smaller scale, are used at home for jelly-making, whilst the larger manufacturers installed filter presses. With perfect filtration, such as is obtainable in power presses, all the incriminating cells of the adulterants are removed, only the beneficent “fruit juice” remains, and this cannot be detected by the microscope. In spite of the facilities that were available, however, possibly through careless treatment in manufacture, or because they were willing to run the risk of paying a purely nominal fine, jam-makers were caught occasionally, though the actual sufferer was the retail tradesmen who bore the odium of prosecution. A shortlist of 20 cases occurring during the years 1906 to 1912 may be briefly summarised. In 16 convictions the average fine imposed was a trifle less than £3, which fairly represents the average saving effected by adulteration on one ton of jam. Two defendants (with an average saving of £3. 5s per ton) were let off with a caution, and the remaining two cases were dismissed, the adulteration in one instance being 5%, in the other 15%. If we set aside one case where 100% gooseberry jam was sold for raspberry, probably an oversight, the percentage of adulteration ranged from 50 down to five, with an average of rather more than 15%.
At what state ingenious adulterators introduced the “declaration” on their jam labels cannot be definitely stated, but the device failed as far back as the year 1909, when a judgment in the Divisional Court of King’s Bench was pronounced against an adulterator of coffee (Star Tea Company v. Neale). The tin in which the coffee was sold bore a label stating “This is sold as a mixture of chicory and coffee.” In giving judgment the Lord Chief Justice said, assuming “that he was satisfied that there was a sale with a label saying that the article was mixed, he was met by the further finding that chicory had (in the opinion of the three justices hearing the appeal) been added fraudulently to increase the weight and bulk, and that neither the label, wrapper, nor tickets afforded any protection” to the seller. Coffee and jam are both foodstuffs to which the same Act applies, yet in spite of this clear decision makers relied, and usually with success, upon the “disclosure by label” defence, and such wording as “Improved by the juices of other choice fruit” continued in use on jam labels.
However, the matter was not allowed to drop, and four years later something in the nature of a test case was fought over “improved” jams (St. Marylebone Borough Council v. Rapson) before Mr Paul Taylor. In a long considered judgment the magistrate said: – “I find that under section 8 (Food and Drugs Act) the disclosure label was not the disclosure contemplated by statute, and therefore has not been established in such manner as to protect the seller.” Notice of appeal was given, and pending the hearing of the appeal similar cases were left in abeyance. In the end the appeal was abandoned, and not long after war broke out and obscured this along with many other issues. In fact, adulteration may almost be said to have been legalised when Army contractors were allowed to add a percentage of other fruit juices to the jams supplied.
Careful study of makers’ labels has a humorous as well as a useful side. It is generally only the more expensive jams that can be “improved,” and invariably the improvement is brought about by the admixture of a cheaper fruit. Who has ever seen a pot of apple jam stated to be improved by the addition of raspberry juice! When plums are scarce and apples plentiful, “improved” plum jam may be sought successfully, whilst when the position is reversed the buyer of a fine “improved” jam may unawares have the pure article fobbed off on him if the maker is not conscientious enough to alter the wording of his labels. Another amusing little catch is the “guarantee” that the jam “is made solely from the fresh fruit and finest sugar” – no doubt, but what fruit? After all, the remedy for the unsatisfactory state of affairs rests largely with the purchaser; he or she should refuse to buy jams that are not labelled “jam,” raspberry jam or plum jam, for example, and should leave all “improvements” alone.
During the war starch-sugar or glucose was officially put forward as a useful preserving agent, though previously it occupied an ambiguous position. Some authorities held that as a form of sugar it was permissible in jams, others, including many analysts, that it was added “to increase the bulk” of the preserve and was consequently an adulterant. It is quite easy to find by chemical means in conjunction with the polarimeter the percentage of starch glucose in jam, but Lord Alverstone’s judgment in regard to glucose in marmalade (Smith v. Wisden) stands in the way of a successful prosecution. Some research was applied during the war to the possibility of obtaining pectin from spent cider apples, thus securing food from waste products; whether the process was a commercial success is unknown to the writer. If obtainable at a reasonable price and free from any tell-tale chemical traces of its preparation, pectin might, like carefully prepared fruit juice, be immune from detection. Passing over animal gelatin, which is seldom if ever present in a commercial jam, we come to agar-agar. Undoubtedly here is an excellent adulterant, for at a low concentration, about 2%, a good structureless jelly is obtained. Characteristic diatoms abound in this seaweed and may be found in jams; strawberry jam is as likely as any to contain this adulterant.
I am, &c.,
3, Park-villas, Loughton, Essex.
I am sure that all this detailed knowledge must come from long-term employment in the jam industry.
It took quite a bit of digging and finally some luck to track down where he worked.
At the beginning of 1890 Ernest and his father bought out the partners of Hogarth & Co., Aberdeen Works, 77-83 High Street, Stratford, east London. The previous owners, the Maltby family, sold the business as a going concern to the Marriages. I assume that James Marriage was the Managing Director and Ernest the Technical Director, at least in practice.
The business continued under their ownership until it finally closed in the 1920s, by which time James had died (in 1913) and Ernest was about 60 years old.
We are fortunate that Charles Booth was active in the area at the time of the change of ownership. Booth was a well-known social reformer, who produced the 17-volume Life and Labour of the People in London, with the final version appearing in 1902-3. He and his team interviewed large numbers of people and businesses, and Hogarth & Co was one of them. His interview notes are preserved, so we can see what went on there around the time of the Marriage takeover.
Interview with Messrs. Hogarth and Co. of High Street, Stratford:
Men – four jam boilers. Foremen in the jam room, women carrying etc under them.
Two sweet boilers – same class of skill.
11 packing and carting. Fixed wages 45/-, 35/-, 30/-
Women piece workers – 30 earn 15/-, four earn 13/-. Day workers – ten at 10/- and 13 at 8/-, the latter merely carrying boxes etc from filling rooms to carts etc. Others engaged at filling, labelling, varnishing tins for export etc.
The export jam is all in tins except when the purchaser takes the risk.
Payment by piecework found more convenient than regular wage because there is no dispute about raising the wages. If a complaint as to earnings should arise the complainant is told that she should work quicker and so earn more. The 13/- to 15/- are “young ladies”, the 8/- to 10/- are “xxx”.
Packing made of fine strips of wood – nearly double the cost of straw and yet cheaper in the end.
Jam making – fruit in tins, e.g. apricots from France, Spain, Portugal and Italy, also the Balearic Isles – used to come from California too, but cost more and considered not worth the difference. These apricots have been merely boiled and sent out in tins. They are placed in the boiling pans, heated by steam and sugar added. In the soft fruit season crowds of women employed picking stalks the whole fruit jams. For ordinary jam a machine is used to separate stalks and stones from the soft substance.
Pickling. Better pay than jam making because harder work, especially in winter when vegetables, which have to be kept out in the cold, are handled with vinegar which stings the chapped hands. Filling bottles with mixed pickles is better paid than filling bottles with onions or cabbage. The mixed pickles have to be artistically arranged with the same proportions of each kind in the xxx bottles. Onions are most expensive to pickle – consequently in a bottle of pickles every onion is always visible from the outside though perhaps the cabbage may fill up the middle – an onion is never allowed to enjoy oblivion.
Busy all year round because export trade to the Cape and Australia in English summer.
Sweet making – in pans over fire, the steam process used in jam making is not powerful enough for sweets. Busiest time it is winter. When hot weather begins youngsters prefer to spend their pennies on Sherbert and drinks.
Bottles made in France and Belgium. Large bottles made in England because freight smashes them. Curious superstition that magnesia must be in blue bottles, no reason for it except people won’t buy it if in any other bottle.
Lime juice and lemon juice. Former is bright and latter cloudy. Sometimes people ask that lemon juice should be clear. As matter of fact the juice of a lemon is bound to be cloudy. Hence some makers advertise “our lemon juice is not bright”. Another advertiser “our lemon juice is the only bright juice in the trade”.
Royal Photographic Society
Held at 35 Russell Square W.C., on Tuesday, October 21st, 1913, Mr. Chapman Jones, F.I.C., F.C.S., President, in the Chair.
The Minutes of the previous Technical Meeting were read and confirmed.
The president called attention to the house exhibition of photographs by members of the Nature Photographic Society, which had been opened to the public on the previous day, and expressed the pleasure of the Society at affording opportunity for the display.
The following paper was read by the author :—
PHOTOMICROGRAPHY AND JAM ADULTERATION.
By Ernest Marriage, F.R.P.S.
If there is any ready means by which adulteration may be suspected, a sort of signpost in fact pointing to the fraudulent article, it is a saving of time to know it. That sign-post we have in the wording of manufacturers’ labels : if these display, or rather perhaps conceal, somewhere in the wording that the jam is “improved by the addition of fruit juice” or “improved by the addition of other choice fruit,” it may be taken as certain that the jam is adulterated, in the one case with the filtered juice of apples or gooseberries, in the other with apples or gooseberries rubbed through a machine sieve to extract core and pips. In either case the reason for the addition is the same: the fruit is cheaper than that to which it is added. The advantage of filtering is that it renders the detection of the fraud more difficult; filtering costs money, so some makers prefer to “chance their luck” and use pulp. Another indication worth following is the omission of the word “jam” from the label on the pot. “Strawberries preserved whole” (see Fig 1) for example, may be and often is strawberry and gooseberry jam, which if called by its right name is not so easily saleable; the housekeeper wants strawberry jam and that is how a cheaper mixture is palmed off upon her.
The general public have weird notions as to the adulterants employed by makers. This is partly due to a morbid craving for excitement, people like their hair to stand on end or their flesh to creep and the journalists supply their needs. Carrots, turnips and mangel-wurzels, though wholesome harmless vegetables, give the desired shock, where mention of the regular fruit adulterants leaves the hearer cold. The mainstay of adulterators is apple, though green gooseberries are also widely used. Other fruits are open to drawbacks, red currants are not sufficiently cheap as a rule to “improve” the more costly jams; lemons, after the skin has been removed are cheap, but if used in quantity give the jam a bitter taste. Rhubarb is cheap, and I have a label of raspberry and apple jam “improved by a judicious admixture of rhubarb.” Occasionally seeds other than those of the fruit are used. Two or three years back sesame seeds were found in a raspberry jam that was also “improved” with apple and gooseberry. I suppose the addition of the latter fruits deprived of their pips created a deficiency in the jam which the sesame seeds were intended to cover, but the fraud is very easily found by the microscope. If detection is easy in the case of the addition of another seed, what chance would the mythical wooden pip stand against any microscopist? Figs have been added to strawberry jam; the seeds are similar in size and shape, but the strawberry seed has markings on its surface which are absent from those of the fig.
Circumstances render it undesirable for me to show you specimens or photographs of actual labels. Any of you who are sufficiently interested can pick out “improved” labels in the window of the nearest grocer’s shop, particularly in the case of strawberry or raspberry jam. Nor do I propose to go into the legal aspects of the fraud beyond saying that the “improvement” is always cheaper in actual use than the fruit “improved”. Another essential is that the flavour of the adulterant shall not be strong, otherwise it would be detected at once in the blended jam. An improved jam is therefore both cheaper to produce and inferior in flavour to the pure article; in the face of these facts how is it possible to maintain that the word “improvement” is not absolutely synonymous with adulteration?
Two difficulties stand in the way of those who would if they could stop adulteration – It is not possible by a purely chemical analysis to detect these adulterations. The adulterant is harmless, as wholesome probably as the pure article, so magistrates fail to see much or any harm in the swindle and either dismiss cases or impose nominal fines. A few £20 fines would do more than anything else to put an end to this dishonest trading.
However, when chemical analysis fails, the microscopist steps in, and detects the cells of the various constituents in a faked or “improved” jam. When I first took up this branch of work, about three years ago, I borrowed a microscope from a friend, quite lightheartedly, expecting to return his instrument in a fortnight. Three or four months later I began arranging a photomicrographic plant of my own. The illuminant will no doubt vary with the local conditions; electric current not being available, I find incandescent gas the most convenient light and use a bijou burner of good quality and a high-class mantle. The bullseye condenser takes the form of a 3-inch portrait lens, which was bought cheaply second hand. It answers the purpose admirably; being achromatic and comparatively free from spherical aberration, it should and no doubt does give better results than the simple bullseye.
Coming next to the microscope itself, a substage condenser is required, which should, of course, be achromatic. The Zeiss achromatic condenser answers for much of the work, though for ¼-inch objectives and higher powers or even a ½ -inch with big aperture, its aplanatic cone is rather too small for the best results.
The objective with which most of my work at low magnifications is done is a Reichert 3/5-inch N.A. 30, used in conjunction with a low-power Huyghenian (x 2½ ) eyepiece. In order that records may be easily comparable it is desirable to work at a standard magnification; 75 diameters is a useful enlargement, working with 5×4 plates My camera has an extension of about 22 inches and is designed for 7½ x 5 plates: the extra size is no drawback and in fact diminishes the risk from internal reflections. With this combination of objective and eyepiece, a range of between 50 x and 120 x can be usefully obtained. For higher magnifications another eyepiece could be employed, but it is better to change the objective for one of higher power and larger aperture. Fig. 2 is an example of work done by transmitted light.
Colour screens, particularly a blue screen, may be usefully employed to accentuate the walls of fruit cells. For contrast the screen should be a complementary colour, to reduce contrast the screen should match the colour of the object.
Very frequently the fruit cells are colourless and only very faintly visible by transmitted light; recourse may then be had to dark ground illumination. This can be obtained by putting a suitable central stop in the substage condenser, by special forms of condenser, such as a spot lens, or by a parabolic reflector. Of the three I use the last, it gives a better dark ground than the condenser with a stop, but I have not compared it with a spot lens. This method of illumination requires increased exposures. Whereas a photomicrograph of a jam taken by transmitted light at 75 diameters may require a minute or less, 15 minutes’ exposure is wanted, in my experience, for dark ground illumination.
A third method of lighting, and the best, is that obtained with the polariscope and crossed Nicols, but as a large amount of light is cut out exposures have to be increased considerably. The polariser is fitted into the mount of the substage condenser as close to the iris diaphragm as possible, in other respects the arrangements for illuminating the slide are the same as for ordinary transmitted light. The analyser in my instrument fits on the eyepiece so that I have to adjust the amount of rotation before placing the camera in position. The polariscope emphasizes differences in the structure of almost transparent substances, such as small fruit cells, far more than is possible with either ordinary transmitted light or dark ground illumination. Exposures of less than one hour are useless. A record obtained by this method is shown in Fig. 1.
In the discussion following a paper which I read before the Royal Society of Arts in February last, Mr. Alfred W. Stokes, F.I.C, F.C.S called my attention to the usefulness of iodine as a test for apple in jams, and subsequently kindly gave me a demonstration of the method he adopted. It is based on the fact that a large proportion of apple cells contain starch which on the application of a solution of iodine is turned to a deep blue colour. If a thin section of uncooked apple, stained with iodine, is viewed in the microscope, the starch granules, now a dark blue, will be plainly seen.
Apple cells maintain their shape even after boiling, so though the heat breaks up the starch granules they are only diffused in the cells and the apple cells in a jam are stained blue. Another fruit which contains starch is the vegetable marrow, but I believe its use is confined to amateur jam makers.
One of the difficulties in making records of jam adulteration is to show details of the original fruit and the adulterant together. To do more than this, to represent fairly the proportion of the various ingredients, is impossible with even a moderate magnification. Something can, however, be done in this direction in the case of an apple adulterant by means of the iodine test and a lens giving a low magnification such as one of the Zeiss Micro Planars or the recently introduced Aldis Photomicro-graphic lenses. Fig. 3 shows comparative tests obtained in this way of an improved and a pure raspberry jam, the pure above, the faked below, a reversal of the regular commercial order where the adulterated article, by virtue of its price, generally comes out on top. The apple cells in the adulterated jam show as dark oval spots, and by their frequency an idea of the extent of the adulteration in this sample can be arrived at. The magnification is 3 2/3 diameters and two halves of ¾ -inch circular slides are reproduced.
Some little time ago there was a prosecution in London in connection with an “improved” raspberry jam. The usual plea that an accident had happened in the factory was put forward by the manufacturer, who brought witnesses to swear to that effect. My own opinion is that these accidents recur rather than occur, so I bought a pot of jam from the same factory, but in a city 100 miles and more from London, where the prosecution arose. There was apple in my pot also. One would be loth to believe that a philanthropist who benefits the public by improving his jam would unmoved hear his employees perjuring themselves, so I can only conclude that my sample and that bought 100 miles away by a London inspector formed part of that identical boil of jam. They do say “truth is stranger than fiction.” Perhaps for the-benefit of the uninitiated it will be well to mention that a boil of jam may weigh about1 cwt., whilst there are many makers who use small steam pans that only turn out halt this quantity at a time.
The “improved” raspberry jam in Fig 3 is a record of this case.
Regarding the preparation of microscopic slides for examination, after experimenting on a variety of methods the following seems the best :— A small piece of jam, free from seeds, is placed on the centre of a clean slip, a clean ¾ -inch cover glass laid on the top and pressed down until the jam layer is as thin as possible, a clean 3/8 cork is handy for this purpose. There should be a ring of jam all round the cover glass on the slip: leave the slide to dry for a day or two, then remove any excess of jam there may be, being careful, however, to leave a little all round the cover glass. Traces of jam on the slip are of no consequence. Place the slide on a turntable and ring it up to the edge of the cover over the remaining jam with a syrupy solution of gum arabic containing some carbolic as a preservative. In the course of a day or two the gum combined with the jam will set hard. A ring of waterproof varnish may now be applied; when that is dry the surplus gum and jam can be washed off the slide with the aid of water and a brush; the slide is put aside to dry again, and a coat or two of varnish or gold size, extending slightly beyond the first ring, so as to cover the exposed edge of gum, completes the work.
So far no account has been taken of filtered adulterants, that is, fruit jelly or fruit juices. Scientific filtration can remove all the tell-tale vegetable debris, in which case a purely optical examination is of very little use. A good deal of adulteration goes on in jam making to-day which escapes detection. If filtration has been thorough, the maker need not even trouble to say he has “improved” his jam, which is a dodge for evading prosecution, he simply defies detection. We now arrive at the point where purely chemical and purely microscopical analysis fails but by a combination, by micro-chemical tests, something further can be done. In this connection I must acknowledge my indebtedness to Mr. Emil Hatschek, whose first course of lectures on Colloids at the Sir John Cass Institute I attended in the winter session of 1911. He pointed out that the forms assumed by a number of insoluble salts varied according to the gels in which their precipitation takes place (see The Journal of the Society of Chemical Industry, March 15th, 1911, No. 5, Vol. XXX). At his suggestion I undertook a series of experiments on the lead iodide reaction in a number of fruit and other jellies.
The method I have adopted is as follows :—The jam to be examined is diluted to a strength of 1 in 10 and filtered whilst hot with a suction filter. It is important to get rid of the vegetable fibres, so the filtration of the adulterant by the manufacturer is a help rather than a bar to detection by this method. The filtered solution is reboiled to a standard temperature—I worked to 230 degrees Fahrenheit—and 5 per cent of potassium iodide is added. The jelly is then poured into test tubes (a depth of 2 inches is sufficient) and when it is cold and has set, a 20 per cent, solution of lead nitrate is gently poured in on top of the jelly. A dense yellow precipitate of lead iodide is formed, which gradually extends downwards in the jelly. The reaction in the presence of sugar takes place slowly. At first the lead iodide is precipitated in small particles, but as the reaction proceeds downwards larger aggregates with clear spaces in between are formed, sometimes layers are produced with clearer interspaces, in which case the larger aggregates are in the interspaces, sometimes there is no marked layering. Fig. 4 shows five tests made in this way. Reading from left to right they are apple jelly, apple and gooseberry jelly equal parts, gooseberry jelly, loganberry jelly and raspberry jelly. It will be noted that there are marked differences in the appearance of these test tube cultures, if one may use the term. Apple shows little sign of layering, gooseberry distinct layer formation, whilst the gooseberry and apple is of an intermediate character, and the other jellies are quite distinct.
Something may be learnt from a visual examination of these tube tests, but I think the appearance of the larger aggregates in the tubes is of greater importance. The tubes are broken and a small piece of the jelly containing the larger aggregates is mounted in a cell on a microscopic slip. The best method of lighting these opaque masses perplexed me; as the objects are fairly large (see Fig. 5), and high magnifications are not required, a one-inch objective with a Lieberkuhn may be advantageously used. possibly a silver-side reflector might give a better result. I have not tried this. The lighting given by a Lieberkuhn is powerful, but from the front, which makes it rather difficult to obtain relief in some cases.
An interesting and important problem is: given two jellies which yield differing aggregates, what effect is produced on these aggregates by mixing the two jellies? In the first place it is well to start with colloids that are known to give very different results ; agar agar and starch fulfil this requirement, and as sugar is an important factor in any research on jams both these substances were sweetened for my tests. Turning to Fig. 5 we have first the forms produced in sweetened agar agar jelly: branched aggregates suggestive of plant forms, with rounded surfaces. This subject was taken on a isochromatic plate with a pale yellow screen exposure for x100, 30 minutes. The deposit in starch, the opposite side of Fig. 5, seems to be in the form of thin scales with clearly defined edges. In between are aggregates formed in an equal mixture of the agar and starch jellies, which can be described as intermediate forms.
Unfortunately the differences between aggregates produced in fruit jellies or filtered jams are not so marked ; they are more nearly related than agar agar and starch or gelatine. Fig. 6 shows aggregates from the first three tubes in Fig. 4. Apple, on the left, shows spherical groups of rounded nodules; gooseberry, on the right, yields aggregates apparently built up from flat discs ; in the centre is a culture in a gooseberry and apple jelly.
A serious drawback to these methods of testing is the time taken by the reaction in a jelly containing sugar. The precipitate formed at and near the meeting plane. the surface of the jelly, is dense and fine, it is not until the reaction has passed down some way through the jelly that prominent layers or aggregates make their appearance.
Another method is to produce the reactions in a microscopic slide. The jelly, containing as before, 5 per cent of potassium iodide, is squeezed between a ¾ -inch circular cover glass and a microscope slip, and put in a bath of 10 per cent lead nitrate for twelve hours. At the end of that time the lead iodide will be visible almost to the centre of the circle. Any surplus jelly on the slip can be carefully removed with a brush, the slide is rinsed lightly with distilled water, dried and ringed with old gold size. The brush must not touch the cover glass in putting on the size, and the size should run up to the edge of the cover glass all round to fix it in position. A few more layers of varnish or cement when dried will make the glass firm enough to bear cleaning. The cleaned slide can now be examined and photographed.
We saw that in test tubes marked layers are produced: the corresponding effect in slide tests is that of concentric rings. It is an easy matter to record these with a 2-inch lens such as I have already mentioned. Fig. 7 shows the halves of two tests of pure and ”improved” raspberry jams. The upper semicircle shows the pure jam, and is a very even example of concentric ringing. The impure jam below is not quite so regular, the rings are not as strongly marked, and are broken by radial lines penetrating inwards. The increased separation between the rings as the center is approached is the same in both.
For recording these slide tests the exposure, using incandescent gas and a ground glass diffuser enlarging 5 diameters, was 2 minutes, lens at f/5.6 and an ordinary plate. Or daylight can be employed, in which case the exposures are much reduced ; my records give 13 to 30 seconds, lens at f/8, with a blue screen. I do not think there is any advance in the use of the screen, except perhaps to lengthen exposures for this work – all that is wanted is to show the arrangement of the deposits, which, being yellow are comparatively opaque to an ordinary plate.
The aggregates in these micro slides have not the space to extend freely as in the tubes and are much smaller in consequence. It is better to employ a fairly high magnification and as the aggregates are sufficiently thin to be translucent transmitted light is available. Fig. 8 shows the aggregates in a test slide of pure strawberry jam at 370 diameters : the large scales are typical of those seen in the interspaces, whilst the layers are composed of the smaller opaque aggregates.
As the size and shape of the aggregates is probably conditioned by the limited space in a micro-slide, this method seems less likely to show divergent results than the tube tests; on the other hand, the rapidity of the slide test is in its favour. In my experience it is not possible to preserve these slides for long, so it is desirable to make photographic records soon after they are prepared.
Want of time has prevented me from trying the effect of other reactions. A number of experiments yielding more or less insoluble salts are detailed in Mr. Hatschek’s paper, to which I have given a reference already. I, however, made a few experiments with a barium-silico-fluoride reaction. This yielded comparatively large aggregates of pointed crystals, but the formation was very similar in all the jellies tried. The crystals can be washed out of the jelly and mounted in glycerine jelly, when they make pretty objects for viewing in the polariscope.
Dr. Duncan J. Reid said that he had enjoyed Mr. Marriage’s paper very much indeed. One thing that struck him particularly was the persevering way in which Mr. Marriage had worked at the subject. Many photomicrographers seemed to spend nearly all their time in photographing lovely things, but their lecturer of that evening had made his photographic efforts serve a useful purpose. The same remark applied to his use of the polariscope. Results with the polariscope were usually shown something to be admired, but Mr. Marriage had made use of the effects in a practical way. Mr. Marriage had spoken of his work as still incomplete, but judging by the progress he had already made, the speaker imagined that jam-makers would : rather he came to a standstill.
Mr. W. B. Ferguson said there was one scientific point that struck him in Mr. Marriage’s lecture, and he would like to know to what was attributable the periodicity of the rings which resulted from the chemical reactions in the test tube. Why, instead of getting a gradual percolation of the nitrate of lead into the iodide of potassium did one have this phenomenon of the alternation of dense and transparent layers ? This, perhaps, was rather a question of chemical physics than one of photography.
Mr. A. W. Stokes, F.I.C., said that Mr. Marriage had very kindly alluded in a part of his lecture to some analytical work of his (the speaker’s) own, and that must be his excuse for rising, chiefly to say how greatly he admired the perseverance which Mr. Marriage had brought to the subject. He was specially pleased to hear that he had gone a little further into his subject since his lecture at the Society of Arts. Speaking as an analyst, he must say that they did not always rely upon the findings of the microscope, but made quantitative tests for the adulterant. They took a certain quantity, weight or volume, of the material, and separated and counted the skins, or, in such jams as raspberry, the seeds. By this method of counting and comparing genuine with non-genuine jams, they could form a notion as to any adulteration, independently of the microscopical appearances, although, of course, this method was not possible when they came to preparations which had neither pips nor skin. The speaker went on to explain a method, useful when one was in a hurry, of mounting jam samples in series of dozens with the aid of cements, and said that he had mounted hundreds of slides of colloids and jams in that way. Take, say a dozen, microscopical slips ; on a turn-table run a ring on each of these with gold-size or marine-glue, etc., slightly smaller than the cover-glass you intend to use. By the time you have ringed the twelfth the first will be tacky enough for you to fill it with the jam or other fluid. Now put on the cover-glass with a slight spring-clip to force out the excess of jam.
When the last cover has been put on you can wash the first under the tap, cautiously wipe it and add rings of cement, covering the edge as usual. Even castor oil mounts may be made in this way, washing off the superfluous oil with strong soda. Jam mounts should have a drop of carbolic acid to preserve them. With regard to what the last speaker had said, he (Mr. Stokes) was rather doubtful of tests based on the formation of precipitates in the jelly. These were not characteristic of the various fruits. In his opinion, as a result of experiments, the periodicity of the rings in the tubes with fruit jellies—an aggregation of minute points and then a space—was entirely due to temperature, which varied from day to day and throughout the day and night. The preparation became a little more liquid with heat, and crystals were formed; it cooled down, and there was no crystal formation. He wished that Mr. Marriage would try a few experiments, keeping his tubes at a standard temperature, say in ice, and he believed that he would find that the granular appearance would go down slowly, and instead of being larger at the bottom, he would find it get smaller, because the lead or iodine was being used up. There was a special reason why this would not succeed with jams. In the case, say, of raspberry jam ”improved” by apple, the varying acid-content would exercise an enormous amount of influence upon the crystal to be formed Until the temperature and acidity were eliminated, he did not think that reliable results would be got with regard to these points.
Mr. Whitfield Taylor asked if Mr. Marriage had examined the sweetening agent, and whether starch glucose had any effect on the test.
Mr. H. G. Bailey thought that the quantitative test would scarcely avail in cases where jam manufacturers used the best of the fruit for fruit cordial, and the pulp and pips for jam-making.
The President said that the discussion had drifted away from the photographic aspect of the subject, and although there was no particular reason why the question of adulteration of jams in general should not be discussed if those present desired to do so, he would like to go back to some details that were more in harmony with the objects of the Society. He would like to know whether Mr. Marriage could assure them that different samples of the same genuine jam would give less differences in the photomicrographical results than the differences which were obvious as between a genuine and an adulterated jam. Could the examples of results that Mr. Marriage had shown be taken as truly representative, or what was the amount of possible variation as between different samples of the same jams? Another point related to Mr. Marriage’s photomicrographic apparatus. He was very pleased to see that he had used an old portrait lens instead of a bulls-eye as a secondary condenser. Most of them possessed old and, perhaps, costly lenses that had little market value at the present time, and such lenses, if suitable, would give far better results than bulls-eyes or condensers made especially for microscopical purposes.
Mr. Ernest Marriage, in replying on the discussion, said with regard to the counting of pips as a quantitative method of detecting adulteration, that he himself had counted the pips in raspberry jams, and he found in some instances that the adulterated jam contained more pips than the purer samples. The question of the preparation of the pulp came in very largely in a case like that. If the pulp had been standing for some time before it was ladled out into the jam boiling pans, the pips were liable to have settled, with the result that there were fewer pips in the earlier boils. Mr. Bailey’s suggestion might account for the surplus of pips in the “improved” jam, and this at once threw doubt upon the pip-counting method as a quantitative means of analysis. With regard to temperature as a cause of the ringing, surely if it was purely a question of temperature the rings would always be even, but as a matter of fact they differed very largely, and the rings increased in separation the lower one got down into the jelly.* He could not offer any theory on this point. Mr. Taylor had asked him whether the use of starch glucose had any effect upon the test. He did not think it had. He had tested jams containing a proportion of glucose, and jams containing only cane sugar, and he did not find any difference in the results. The President had asked whether the results shown were truly representative. The speaker considered that on the whole they were, but he had come across very divergent results with the same kind of jam made in two ways, and that was a puzzle to him. He had shown on the screen some tubes containing raspberry jam—one from fresh fruit and one from fruit stored in the form of pulp, and there was a distinct difference between the two. In the fresh fruit there were marked layers with transparent interspaces, and in the pulp the layering was not so marked. When examined under the microscope the aggregates were exactly the same in form in both cases, quite round aggregates, and of much the same size at the same depth. He was glad to have the President’s commendation with regard to the portrait lens. It was a 3-inch Darlot lens which he had picked up second-hand for half-a-guinea, and he had had an iris diaphragm fitted to it, and found it answer the purpose admirably. It gave far less spherical and chromatic aberration than the uncorrected bulls-eye.
A vote of thanks was carried with acclamation on the motion of the President, who said that Mr. Marriage had brought before them some interesting and suggestive researches which at least formed a substantial start.
* A practical refutation of the suggestion that ringing or layering is due to variations in temperature is provided in Fig. 7. These and similar slides were produced by immersion in a bath containing 2 oz.of solution, which was covered with a sheet of glass, conditions which would make any change of temperature gradual and even, the period of immersion being less than twenty-four hours. So long as the changes of temperature occur below the melting point of the gel I doubt if the formation of the aggregates is materially affected. The state of concentration of the invading solution (in my examples lead nitrate), which is affected by the distance travelled through the gel, is of much greater importance.— E.M.