DETECTION OF THICKENERS IN ICE CREAM.

By G. E. PATRICK.

The thickeners commonly used for ice cream to-day are gelatin, certain vegetable gums or jellies, and various forms of starch. Of the true vegetable substances gum tragacanth is most used, and it is believed that at least one other substance of this class is employed, but it was impossible to tell whether it was agar or some less common member of the group.

A test for the detection of such thickeners has been formulated which it is believed will prove useful if the conditions are closely observed, the main features of the method offering little that is new from a chemical point of view. Picric acid is used for precipitating gelatin, and alcohol for the gums. Preparatory to the test the liquid is clarified by coagulating the proteids with acid and heat and filtering. The details of the procedure, elaborated with the help of H. S. Bailey and B. McClelland, of the Dairy Laboratory, are as follows:

To 50 cc of ice cream add 25 cc of water, boil for half a minute to dissolve any thickener that may be present, add 2 cc of a 10 per cent solution of acetic acid, heat again just to boiling, add two or three heaping teaspoonfuls of kieselguhr, shake well, and filter immediately through a plaited filter. To 3 cc of the clear filtrate add 12 cc of 95 per cent alcohol and mix; this precipitates the milk proteids not removed in the clarification, together with the gums, and some of the gelatin, if much be present; add 3 cc of acidified alcohol prepared by mixing 95 cc of 95 per cent alcohol and 5 cc of concentrated hydrochloric acid; this dissolves the milk proteids completely. If the liquid is clear after this treatment, no gums or vegetable jellies are present. But, on the other hand, turbidity or a precipitate does not necessarily indicate the presence of a thickener; for this may be caused by the large amount of gelatin present or by eggs (more than three or four per gallon), or because the ice cream has become sour. Fortunately the precipitate due to gelatin or to the substance derived from eggs can be readily dissolved by a moderate dilution of the alcohol with water, for instance, by 3 cc of water in the test just described. This amount of water does not sensibly dissolve any precipitate due to vegetable gums or jellies, but entirely dissolves that due to gelatin and eggs. If gum tragacanth is present, the precipitate will be cohesive and stringy, or will become so upon shaking; while if the undissolved matter is due to other vegetable thickeners (possibly agar), it is finely flocculent and devoid of cohesive property.

If the ice cream is sour, there is sometimes a precipitate of another character, which must be derived chiefly, if not entirely, from the cane sugar present, since it appears very faintly, if at all, in tests upon unsweetened milks that have been allowed to sour. But this substance does not always develop in sour ice creams or in sweetened milks that have become sour; its appearance seems to depend upon some special property or condition of the milk, probably upon the presence of certain kinds of bacteria. Its nature is now being investigated, and Mr. C. A. Browne suggests that it may prove to be dextran. Whatever it may be, the precipitate which it yields with alcohol is not sensibly dissolved either by the acidified alcohol or by the water added to dissolve the gelatin and egg substance; therefore it must remain mixed with the vegetable gums and jellies. It does not resemble gum tragacanth, as it is not stringy, but does closely resemble the other vegetable thickener. It is therefore a serious obstacle in the test. Fortunately, however, its formation appears to be prevented by formaldehyde (experiments on this point are still in progress), and it is believed that if fresh ice cream is treated with a liberal dose of formalin there will be no trouble from this annoying substance even if the test is carried out several weeks later.

The test for the detection of gelatin was made on a small portion of diluted cream after boiling but before acidifying to precipitate proteids. The provi

sional method of the association, originally published by Stokes (Analyst, 1837, p. 320), was used, which consists in clarifying the milk or cream with dilute mercuric nitrate solution and precipitating the gelatin in the filtrate with picric acid. It is in general a satisfactory test. But the interesting fact was observed by Mr. Bailey that in testing ice cream which had been sour for a week or more, or very sour milk, whether previously sugared or not, picric acid produces a yellow precipitate easily mistaken for that produced with gelatin. No way of distinguishing between the two has been found, but, as would be expected, formaldehyde prevents the formation of this "pseudo gelatin and therefore samples thoroughly preserved with formalin present no difficulty from this source. Starch, often used in a mixture with gum tragacanth, and sometimes alone, was detected in the usual way with iodin, using a portion of the boiled diluted sample.

REPORT ON THE DETERMINATION OF WATER IN FOODS.

By F. C. WEBER, Associate Referee.

The referee regrets that a full and definite report on this subject can not be given this year owing to lack of cooperation and of sufficient time to devote to the work. Circular letters were sent to 15 chemists asking for their collaboration; only 5 replied, stating that they could not take up the work this year. The results obtained this year showed that drying in a vacuum of 0 to 5 mm of mercury over sulphuric acid compared favorably with drying in an oven with partial vacuum at 100° C. The results, however, in the vacuum oven were obtained in ten hours, while nine days were required to get the same results in the vacuum desiccator. The addition of phosphoric anhydrid as an auxiliary drying agent in the vacuum-desiccator method did not appear to shorten the time of drying. From the somewhat limited amount of work which has been done so far, the referee does not feel justified in condemning the method, though it is doubtful whether it could, even when modified, come into general use. The importance of further study on this subject is recognized, and it is therefore respectfully recommended that the work be continued next year.

THE CARBON DIOXID VALUE OF PURE COMPRESSED YEAST AND COMPRESSED YEAST AND STARCH COMPOUNDS.

By T. J. BRYAN.

The examination of numerous samples of compressed yeast in this laboratory showed that the majority of them contained added starch, usually either potato or corn starch.

The question arose, What is the value of the pure compressed yeast to the consumer as compared to the article mixed with starch? Some preliminary experiments were made, using samples of pure compressed yeast and yeast containing corn starch, such as were found on the market. In these preliminary tests the different yeasts were allowed to act upon a 10 per cent sugar solution and the volume of gas generated was measured. The results showed that the pure yeast had a greater carbon dioxid value than yeast mixed with starch. Owing to the size of the apparatus necessary for collecting and measuring the volume of the gas produced, it was thought better, in subsequent experiments, to determine the amount of carbon dioxid gas produced by the loss in weight. Furthermore, as the different yeasts tested were made by different manufacturers from different cultures, it was decided that the results secured were of little value in deciding the effect of the presence of starch in compressed yeast, and that samples of yeast from the same culture must be

secured, a portion of which should be kept in the pure state, and other portions mixed with potato and corn starch.

Seventy pounds of this pure yeast were mixed with 10 pounds of corn starch and 16 pounds of water (it was found necessary to add the water to make the mixing uniform and in order to produce a cake). To another portion of 70 pounds of the yeast were added 10 pounds of potato starch and 19 pounds of water. To the remaining portion of pure yeast no starch was added in the mixing. These three samples were then pressed separately and cut into 1-pound cakes which were each dipped in water before being wrapped, as is the custom of the manufacturer. These three samples were then allowed to act upon 100 cc of a 10 per cent sugar solution to which 75 cc of water had been added in an Erlenmeyer flask of about 190 cc capacity. This flask was provided with a calcium chlorid tube adjusted by means of a cork in order to prevent loss of weight by evaporation. Two grams of yeast were used in each test and duplicates were run. The flasks were put in a box, the opening of which was covered with a towel and placed against the chimney where a temperature varying between 20 and 30° C. was maintained. During the last three days the box was replaced by a section of a bookcase and the temperature maintained ran a little higher than on the preceding days, varying between 25° and 30° C. Owing to the varying temperatures on different days only the results for the same periods on the same day are comparable. The flasks were weighed when they had been filled with the reagents and once every hour after that for ten hours, and again at the end of each twenty-four hours. Acknowledgments are due to Messrs. Nehls and Gardner and Mrs. M. B. Shulda for assistance in making the tests.

Table I shows the average loss in weight for the periods specified. Table II shows the average per cent of loss in weight (or the percentage of the weight of carbon dioxid gas produced for the specified periods), considering that the average weight of carbon dioxid produced by the pure yeast samples for each period is 100 per cent. It will be noted that after two hours the average loss in weight of the flasks containing pure yeast is, with a single exception, greater at every weighing.

The average percentages of the yield of carbon dioxid gas for twenty-four hours and for six hours, as given in Table II, show conclusively that the effect of starch upon yeast is to reduce the carbon dioxid value and that this percentage reduction is greater than the percentage of starch used in preparing the samples. It has been claimed by some manufacturers that it is necessary to use starch in compressed yeast in order to preserve the same. The data in Table II show that on the fourteenth day the value of the pure yeast is greater than on the first day as compared with both of the starch yeast mixtures. The differences, however, are not sufficient, in the writer's opinion to justify the statement that the yeasts containing starch had deteriorated, though the data point in that direction. As fourteen days is a longer time than compressed yeast is kept before being put on the market and used the.contention that starch is necessary to preserve yeast is seen to be absolutely false. Nineteen days after the yeast was prepared all of the samples were perfectly sweet.

It was thought desirable to test the action of these different yeasts in the making of bread. The bread was made with 650 grams of flour, 500 grams of water, and 10 grams of yeast or yeast starch mixture. On the second day pure yeast yielded bread having a volume of 2,225 cc; corn-starch yeast mixture, bread 2,100 cc in volume. On the fifth day pure yeast yielded bread of a volume of 2,000 cc; corn-starch yeast yielded bread 1,860 cc in volume. On the twelfth day pure yeast yielded bread 2,150 cc; corn-starch yeast mixture, bread 2,015 cc. On the thirteenth day pure yeast yielded bread 3,000 ce in volume and corn-starch yeast mixture, bread of 2,575 cc. On the fourteenth day the

bread from the pure yeast had a volume of 2,820 cc, while the corn-starch yeast mixture bread had a volume of 2,650 cc.

As in the action of yeast on sugar solutions, the actual baking tests show that the carbon dioxid value is always greater in the case of pure yeast. By comparison it will be found, however, that the average percentage difference in the size of the loaves is less than the average difference in loss of weight of the sugar solutions for the same periods. This is due to the fact that in the case of the bread it is only the final volumes that are compared, whereas to make the results comparable with those obtained by the action of yeast on sugar solutions it would be necessary to determine the difference in volume (for 2 grams of yeast) between the freshly mixed bread and the final volume of the loaf. There is much work to be done before the action of starch in yeast will be known in all its details. The writer feels, however, that the results here given are sufficient to justify the statement that starch in compressed yeast is an adulteration. The advantage to the manufacturer is easily seen when we consider that he sells starch which costs less than 3 cents per pound at the price of yeast which costs 15 cents per pound. A standard for compressed yeast that will exclude the use of added starch is therefore most desirable. Next to the quality of the flour the quality of the yeast is of prime importance to the 70,000,000 people of this country in the preparation of their bread.

TABLE I.—Average loss in weight of sugar solution containing pure yeast and yeast-starch mixtures, September 19 to October 2, 1907.

TABLE II.-Carbon dioxid gas produced in sugar solutions containing yeaststarch mixtures as compared with those containing pure yeast, rated at 100.

Vice-President Snyder took the chair at this point and Mr. J. P. Street delivered the annual presidential address.

PRESIDENT'S ADDRESS.

By J. P. STREET.

Gentlemen of the Association: An unfortunate unwritten law, supported by the custom of many years, demands an address from your presiding officer. My 23 predecessors have covered the ground so well, and have appreciated the merits and the failings of this association so thoroughly, that there is but little left for me to do save to repeat their congratulations and emphasize their warnings.

That the original object of this association was to secure uniform and accurate methods for the analysis of fertilizers is known to you all. Likewise you are all familiar with our steady growth, until now we include within the province of our study and control practically all materials connected with agricultural industry. This widening of the association's activities has limited in some degree the interest of the members in its work as a whole. This is an inevitable result of our expansion, and, deplorable as it is from certain points of view, it could not be expected that either time, inclination, or immediate interest would lead all the members to take part in all the work. This is no reason, however. why every member should not take part in some of the cooperative work each year, and by his careful work help in the solution of the numerous problems that still confront the agricultural chemist. In the association's earlier days it was the custom for practically every institution represented in its membership to share in the cooperative work, and this was easily possible when fertilizers alone were the subject of study. It was also the custom then that this work should be performed by the experienced men of the staff, so that when the results were presented to the referee for comparison and study they would furnish a reasonable test of the method's accuracy, and not of the capability of the analysts. But in later years this condition to a great extent changed; the official samples all too often were used to check the younger assistants rather than the method itself. This resulted in certain cases in injustice to methods which proved later to be thoroughly dependable, and it would seem that the publication of certain of the comparative results must have had a harmful effect on our standing as an association. It is a matter of deep gratification,