seems to be no objection to the use of the excess of phosphoric acid in this case, it is thought advisable to recommend a uniform quantity of phosphoric acid which will answer for all purposes. (3) Page 90, after line 34, insert "Instead of titrating the excess of iodin with the standardized thiosulphate solution, the sulphurous acid distilled over may be determined directly by acidifying the iodin solution or an aliquot thereof with hydrochloric acid, boiling until colorless and precipitating sulphuric acid in the usual way with barium chlorid.” (4) Page 110, line 41, transpose the phrase "boiled to expel carbon dioxid" to line 40, inserting the same after the word "pink." (5) Under method for boric acid insert the following method: Weigh about 50 grams, make alkaline with milk of lime, evaporate to dryness and ash. Dissolve in hydrochloric acid, filter and wash. In case much carbon remains, burn the paper and residue after making alkaline with milk of lime and treat with hydrochloric acid as above. Make the filtrates alkaline with sodium hydroxid, boil, add barium hydroxid until no further precipitate is formed, and filter. Dissolve the precipitate in dilute hydrochloric acid and reprecipitate with sodium hydroxid with the addition of a few drops of barium hydroxid. Wash the precipitate with hot water, cool the filtrates and washings to room temperature, and dilute to definite volume. Take an aliquot portion, add methyl orange, and acidify. Boil to expel carbon dioxid, cool and add decinormal alkali until the pink color is just discharged. Add 5 or 6 grams of mannite and a few drops of phenolphthalein and titrate the boric acid, which is now all in the free state, with decinormal alkali. When the end point is obtained it is well to add more mannite to be sure that enough has been used. (6) Eliminate from methods for salicylic acid directions to extract the residue with gasolene. (7) Page 73, eliminate the resorcin method for formaldehyde, inasmuch as this method is unreliable and there are better ones available. It is further recommended that the referee for the ensuing year conduct work along the following lines: (1) Quantitative determination of salicylic acid in wines. (2) Further experiments for the determination of salicylic acid in fruit products such as jams, marmalades, etc. (3) Further trial of Harry and Mummery's method. (4) Trial of method for the detection and determination of fluorids proposed by Woodman and Talbot (J. Amer. Chem. Soc., 1906, 28: 1437). The privileges of the Cosmos Club were extended to the convention through the secretary of the association, and the meeting adjourned until 2 o'clock. WEDNESDAY AFTERNOON SESSION. REPORT ON DETERMINATION OF WATER IN FOODS. By F. C. WEBER, Associate Referee. The study of this subject by the association was authorized at the 1905 meeting, when a resolution was adopted instructing the referee on food adulteration to provide for the determination of moisture, studying particularly Benedict's vacuum method.a On August 6, 1906, the following circular letter was sent to eleven chemists who had previously signified their interest in this subject, asking their cooperation for the present year: DEAR SIR: At the last meeting of the Association of Official Agricultural Chemists, held at Washington, D. C., November 16-18, 1905, the referee on food adulteration was a Benedict and Manning, Amer. J. Physiol., 1905, 13: 309. instructed to provide for the determination of moisture, studying Benedict's vacuum method and Maquenne's method. Please inform me at your earliest convenience if you can assist in this work, so that samples and instructions can be forwarded as soon as possible. There will be four samples sent out, the moisture to be determined by the methods above and by the method in use in your laboratory. Respectfully, F. C. WEBER, Associate Referee on Food Adulteration. Replies were received from eight chemists, all but two stating that pressure of other duties prevented them from taking up the work at this time, and the two who replied favorably did not send reports. Three collaborators were secured in the Bureau of Chemistry. The samples selected this year were: No. 1. Finely bolted rice flour. No. 2. Durum wheat flour. No. 3. Potato starch, prepared by grinding in a porcelain mortar. The first three samples were in a fine state of division, while the sample of shredded wheat was somewhat coarser. Each sample was thoroughly mixed and allowed to stand at room temperature for twelve hours before being bottled and sealed with paraffin. PREPARATION OF THE VACUUM. Benedict in his original method a employed the Hemple form of desiccator to obtain ' a high vacuum by chemical means. One hundred and fifty to 200 cc of concentrated sulphuric acid are placed in the upper compartment of the desiccator and 10 to 20 cc of anhydrous ether, allowed to flow from a pipette, are placed in the bottom of the lower part. After adjusting the top suction is applied, and when the pressure is diminished sufficiently the ether begins to boil, the vapors forcing out the air within the desiccator. When all the air is removed by the suction, the stopcock is closed and the remaining ether vapor is absorbed by the sulphuric acid. A vacuum of 1 to 4 mm can be obtained by this method in fifteen to twenty minutes. It is essential to have a manometer within the desiccator. It was found advisable to place between the desiccator and the exhaust two wash bottles, the one near the desiccator acting as a trap, while the other contains water through which the ether bubbles, showing the rate at which the system is exhausted. When the water just begins to start back the stopcock on the desiccator is closed. Recently it was found by H. C. Gore b that the Scheibler form of desiccator works equally as well as the Hemple type for the drying of substances in a vacuum. There is no essential difference in the use of these two forms, the sulphuric acid being above the samples in the Hemple desiccator, while in the Scheibler form it is below them. The vacuum is obtained in the same manner, the ether being placed in some convenient receptacle which floats or stands in the sulphuric acid. Inverted ground-glass stoppers, tall enough to be just above the surface of the acid, were found to be quite convenient. Both types of desiccators were used in this work. To avoid errors in weighing samples of this nature in open air, small aluminum dishes, 4.5 cm in diameter and 1.5 cc in depth, provided with a tightly fitting cap of the same material, were employed. It was hoped that a number of collaborators would respond, that a comparison might be made of the various methods employed in different laboratories for determining water in agricultural products. Simple as this determination may seem, it is one of the chief sources of error in the calculation of analytical results. a Benedict and Manning, Amer. Chem. J., 1902, 2: 340. In the third volume of Wiley's Principles and Practice of Agricultural Analysis, 23 pages are devoted to descriptions of methods and apparatus for drying organic bodies. Although the principles involved in each division and subdivision of the methods are practically the same, the application of each method to the same sample would probably give a series of different results, the variations in the details of each method having a marked influence. Carr and Sanborna in 1895, in an exhaustive study on the desiccation of organic liquids, called the attention of the association to the variation in moisture results. They showed that this variation was caused solely by the decomposition and oxidation of the sample and that it was a function of the temperature to which the sample was exposed. By employing a vacuum oven through which a current of dry air passed, they were able to obtain constant results on sugar solutions (levulose) which remained constant after four hours drying. Determinations were made in this work under the following conditions: 1. In a partial vacuum (25′′-28′′) at a temperature of 100° C., through which a slow current of air, dried by passing through sulphuric acid, flowed. 2. In a current of dry hydrogen. 3. In the Hemple and Scheibler vacuum desiccators. Approximately 1 gram samples were used. The nature of this set of samples is such that the first method very likely gives the maximum results in the shortest time of drying. On inspection of the tables this is seen to be the case, and the results of this method are therefore used as a basis for a comparison of the results obtained by the other methods. Weighings were made according to the vacuum method at the end of 24 hours, 48 hours, 3 days, 5 days, 7 days, 12 days, and 20 days. In the determinations made in hydrogen, weighings were made at the end of each hour, the maximum time of heating being from 6 to 8 hours. TABLE 1.-Moisture determinations in duplicate obtained by drying in air for varying 11.62 11.64 11.64 11.64 11.66 11.24 11.45 11.21 11.39 11.44 11.27 11.06 11.20 11.04 11.20 11.23 11.24 3. Potato starch.. 14.65 8.78 4. Shredded wheat 11.27 11.02 11.19 11.04 11.21 11.24 14.50 14.49 14.27 14.46 14.43 14.30 14.48 14.46 9.04 9.24 8.99 9.17 8.94 9.20 9.05 9.20 8.99 9.22 9.02 9.19 9.17 9.20 9.19 In Table 1 are given the results of the determinations made in the vacuum oven, through which a current of dry air passed. The temperature of the oven was kept at a U. S. Dept. Agr., Bureau of Chemistry, Bul. 47, p. 134, "The dehydration of viscous organic liquids." b Designed by Carr; described in Wiley's Principles and Practice of Agricultural Analysis, 3:23. 100° C. and the vaccum at about 25 inches, which corresponds to a water-boiling point of 57°. Thus the water in the samples was exposed to a temperature 43° above the boiling point. Considerable variation is seen in the time of drying employed by different analysts even in this laboratory. Since the kind of material has the greatest influence on the time of drying, this point should be regulated by future work and not be left to the discretion of the analyst. This is seen in sample No. 1, which contains a high percentage of starch, and No. 3, which is pure potato starch, in which cases drying for 2 hours gave practically the same results as drying for 15 hours, while in samples Nos. 2 and 4 there is a smaller percentage of water obtained by drying for a shorter period of time. The relative fineness of the samples also exerts its influence on this point. The determinations in the last two instances in this table were made at a later date than the first two and after the samples had accidentally stood a short time, in the laboratory, unsealed. |