with those obtained by the same collaborator when the sulphuric acidvacuum method was used, thus accounting to a certain extent for the difference in pressure. As with the sulphuric acid-vacuum method, as complete a vacuum as possible is desirable, but can only be obtained by means of a high vacuum pump. Sulphuric acid is slightly volatile in a high vacuum, while lime is not. The preparation of lime presents some difficulty, unless a high temperature muffle is employed, for it is essential that this reagent be carefully prepared by heating for several hours at a high temperature.

Carbide-vacuum method.-This method compares favorably with the sulphuric acid-vacuum method, and with the lime-vacuum method. The drying efficiency of carbide is somewhat less than that of sulphuric acid and about equal to that of lime. Carbide is easily obtainable, very cheap, and requires no further preparation for use. When its usefulness is at an end, it breaks into a fine powder, which can be shaken to the bottom of the desiccator, leaving the clean lumps exposed. The only possible objection to carbide is the acetylene gas which is set free, but apparently this does not act on any of the substances which would ordinarily be dried by this method. Carbide is used to some extent by the writer as a general desiccating reagent; practically the only substances ordinarily encountered in a food laboratory which can not be placed in the carbide desiccator are perforated porcelain crucibles containing cuprous oxid.

Dried apples.-Products of this character can not be dried at a temperature above 70°C. without decomposition. It appears that none of the vacuum desiccator methods removes all of the water, as can be seen by comparing these results with those obtained at 65°C. and 70 millimeter pressure. As determined at 65°C. in partial vacuum, the greatest difference among different collaborators in this product was 1.91 per cent, while slightly better results were obtained by the empirical method of drying for 4 hours at the temperature of boiling water. The greatest difference in this case was 1.46 per cent. The vacuum desiccator methods gave results much lower than either of the heating methods.

It was thought that the method of drying the sample might have some effect on the results of subsequent ether extractions. The writer determined the ether extract on the samples of cottonseed meal, wheat bran, corn meal, and air-dried silage as dried by all of the above methods, and no difference in this result was observed as between samples dried either by heating or desiccator methods. Although these samples did not show a difference in the ether extract with different methods of moisture determinations, some substances, which dry by heating methods to a horn-like residue, give much more satisfactory ether extraction when dried by the desiccator method. This is especially true with meat products and similar substances.

RECOMMENDATIONS.

It is recommended

(1) That the method for the determination of water in foods and feeding stuffs by drying in vacuum over sulphuric acid1 be adopted as official.

(2) That Method E, page 49, for the determination of water by drying over lime in vacuum be adopted as a tentative method, and receive further study in the ensuing year.

(3) That Method F, page 49, for the determination of water by drying over calcium carbide in vacuum be adopted as a tentative method, and receive further study in the ensuing year.

A NEW METHOD FOR MOISTURE DETERMINATION2. By G. F. LIPSCOMB and W. D. HUTCHINS (Clemson Agricultural College, Clemson College, S. C.).

The official method for the determination of moisture in fertilizers is known to be inaccurate generally. For this reason it seemed advisable to develop a method capable of giving more accurate results and requiring a shorter time for each determination. The method worked out in this laboratory is based on combined high and low temperature and vacuum. The sample is heated by means of live steam, and the moisture driven off into a vacuum cooled to 100°C. by a mixture of solid carbon dioxid and ether. The apparatus employed is shown in Fig. 1.

METHOD.

Weigh 1 gram of the material into the bucket, "B". Pass steam from a suitable generator through the jacket, "J", for several minutes, and lower the bucket into place. Adjust the receptacle, "D", containing the freezing mixture, making the joint tight with a little vaseline. After a vacuum has been created, allow the sample to remain in the apparatus 5 minutes; then remove it, cool in a desiccator and weigh. Repeat the process until constant weight is obtained.

EXPERIMENTAL.

Moisture determinations were made according to this method on a number of fertilizer materials, and the results compared with those obtained by the official method, as shown in Table 1.

DISCUSSION.

When cottonseed meal is heated according to the official method it loses its bright yellow color, indicating that some decomposition takes

1 Assoc. Official Agr. Chemists, Methods, 1916, 79.

Presented by R. N. Brackett.

FIG. 1. APPARATUS FOR THE DETERMINATION OF MOISTURE.

H9

place. This does not occur with samples of cottonseed meal treated according to the proposed method. The results obtained by the new method are slightly higher. The average time required for a complete determination is only 25 minutes. In estimations made by both methods the vapor from sodium nitrate gave an acid reaction; that from fish scrap was acid in the official method and neutral in the new method.

CONCLUSION.

In general, the results obtained by the new method are comparable with those of the official method. The new method has the distinct advantage of being extremely rapid and of producing very little decomposition of organic material.

TABLE 1.

Moisture in fertilizer materials, as determined by the new and the official methods.

DOUBLE MOISTURE DETERMINATIONS IN FERTILIZER MATERIALS.

By J. O. CLARKE (U. S. Food and Drug Inspection Station, U. S. Custom House, Savannah, Ga.).

It is a well known fact that the moisture content of many fertilizer materials undergoes considerable change during the grinding and preparation of the sample. This is especially true in materials containing more than 10 per cent of moisture, and is the source of considerable error when the moisture is not determined both before and after preparing the sample for analysis. It has come to the writer's attention that neglect of this point sometimes causes considerable variation in results

reported on the same sample by different laboratories. The apparent error, due to failure to calculate the results back to the original moisture basis, is larger the greater the percentage of the active constituent, and in cases where the active constituent is high, as in muriate of potash, pyrites or some phosphate materials, which contain 40 to 45 per cent of phosphoric acid, a relatively small loss or gain of moisture in the preparation of the sample would considerably affect the reported result.

The writer has secured from a number of fertilizer laboratories the results on several samples of fertilizer materials, such as were found in routine fertilizer analyses when double moisture determinations were made. In most cases results were taken from the records of the laboratory concerned, and illustrate very well the possible error that would have been introduced had double moisture determinations not been made.

Table 1 contains the analytical results on a number of materials on which double moisture determinations were made. In every case except one there was a loss of moisture in the preparation of the sample. One result, however, the last, shows a gain in moisture from 5.85 to 6.85

TABLE 1*.

Variation on active constituent shown by double moisture determinations.

The analytical data from which these tables were calculated was furnished by J. E. Breckenridge, H. D. Haskins, E. W. Magruder, J. H. Parkin, and Paul Rudnick.