Now, my recent experience has been that if the extracted residue be shaken with water and the latter further extracted, an additional quantity of caffein, sometimes equivalent to 10 per cent of the whole, is thus obtained.

Our experience has been a similar one. To illustrate by a specific instance, the residue from twenty hours' extraction with chloroform was shaken with water, filtered, and the aqueous solution extracted four times with chloroform, One-half the chloroform extract was tested for caffein, and gave positive tests with Wagner's reagent and by the "murexid" test. The other portion showed by a Kjeldahl determination 0.0035 gram of caffein, corresponding on the whole sample to about 10 per cent of the amount present.

Görter finds that a considerable proportion of the caffein in coffee is present as a double salt, the potassium caffein chlorogenate, from which the caffein is extracted by dry chloroform only with great difficulty. Whether or not this be the cause of the incomplete extraction, it is evident that the official method needs revision.

Preliminary experiments with the Gomberg method showed it to be practicable for the small amount of caffein (approximately 20 mg) that would be present in the filtrate from the lead caffetannate, providing the volume of solution were not over 25 CC. On account of the slight solubility of the caffein periodid in the wash water it was found best in working with this small amount to suck the precipitate as dry as possible on the gooch filter and not to wash it. Determinations made on 20 mg of caffein in 25 cc of water in this way gave from 98 to 99 per cent of the caffein present Numerous experiments made on the filtrate from the lead caffetannate precipitate by precipitating the lead with hydrogen sulphid and evaporating the filtrate gave fairly concordant results, which were uniformly lower than those given on the same coffee by the other methods for caffein. It was observed that the variations in amount of caffein as determined in this way corresponded roughly with the variations in amount of caffetannic acid as found by the Krug method. Whether these variations and low results are due to incomplete extraction of caffein by the process of digestion employed in the Krug method is a matter which we expect to investigate further.

Görter's method was not given a thorough trial. As far as the work goes it has been satisfactory, and the method is worthy of further trial by the association. It reads briefly as follows:

Eleven grams of the finely powdered coffee are moistened with 3 cc of water and after standing a half hour extracted for three hours in a Soxhlet extractor with chloroform. The extract is evaporated, the residue of fat and caffein treated with hot water, filtered through a cotton plug, and washed with hot water. The filtrate and washings are made up to 55 cc, 50 cc pipetted off and extracted four times with chloroform. This chloroform extract is evaporated in a tared flask and the caffein dried at 100° and weighed.

In the determinations made it has never been possible to weigh the caffein directly on account of impurities, the caffein having been calculated from a determination of nitrogen in each case. From the work done there seems to be a strong probability that a combination of the Gomberg and Görter methods will prove to be the best and most convenient process for determining caffein in coffee.

SECOND DAY.

FRIDAY-MORNING SESSION.

REPORT ON THE DETERMINATION OF NITROGEN.

By CHARLES L. PENNY, Referee.

An apology is due the association for failure to carry out the instructions of 1906 concerning the permanganate methods. Another phase of the nitrogen question considered last year and discussed in correspondence with the National Fertilizer Association seemed to outweigh in importance and urgency all others, namely, the determination of total nitrogen in mixed fertilizers to which nitrate of soda is added. With a view to making a thorough investigation of this subject, the following instructions were sent to such members of this association as were supposed to be interested in the work and to more than a score of analysts named by the secretary of the National Fertilizer Association:

INSTRUCTIONS.

Chemists cooperating in this work are requested to give their attention exclusively to methods applicable in the presence of nitrates, Bulletin 107, page 7 (c), page 8 (d), page 10 (g) and (h). There seems to be urgent need of this investigation, especially since the present methods used to determine nitrate nitrogen have been formally called in question by the representatives of great commercial interests.

No samples are sent herewith, as it is thought that each analyst, by calculating the nitrate used from a solution of nitric acid carefully compared with his own standard alkali and acid, may get more reliable results, through the balancing of possible errors, than from using a common substance.

Let the source of nitrate used be a solution of pure nitric acid, about fifth normal, most accurately titrated against the standard alkali used in the Kjeldahl work. In each case measure accurately into the digestion flask enough of this nitric acid to contain 30 to 50 milligrams of nitrogen.

(1) Follow method (c), disregarding the water in the nitric acid and without neutralizing.

(2) Follow likewise method (d).

(3) Follow method (g), adjusting the proper amount of water, distilling first with magnesia, then with caustic soda and water added to the residue in the distillation flask, collecting separate distillates and titrating each separately.

(4) Similarly follow method (h), beginning in second line "in a distillation flask,”

etc.

If the yield of nitrogen is less than the calculated in (1), (2), (3), or (4), test the residue in distillation flask for nitrates.

(5) Proceed as in (1), (2), (3), (4) with the preliminary addition of 2 grams of cane sugar to the digestion flask.

(6) Proceed as in (1), (2), (3), (4) with the preliminary addition of 1 gram, accurately weighed, of organic nitrogen substance, such as dried blood, fish scrap, or tankage, to the digestion flask. In a separate operation treat 1 gram, accurately weighed, of this added substance similarly except that no nitrate be present; that is, analyze the added substance alone according to (c), (d), (g), and (h). Any nitratefree mixed fertilizer may be used for the added substance.

While the above plan entails much work, it is hoped that a large number of chemists will test at least some of the several official methods in question, if not all. The figures for each separate determination should be reported and the precise method pursued should be fully explained. The results of any other plan of studying the nitrate question, carried out by chemists at their own suggestion, will be welcomed.

Answers were received from five chemists engaged in official work and three engaged in commercial work, viz, Messrs. E. M. Bailey, New Haven, Conn.; F. B. Carpenter, Richmond, Va., reporting work of Mr. W. D. Cooke; H. S. Lansdale, Buffalo, N. Y.; C. B. Morrison, New Haven, Conn.; J. Bernard Robb, Richmond, Va.; B. F. Robertson, Clemson College, S. C.; Paul Rudnick, Chicago, Ill., and T. C. Trescot, Washington, D. C.

It is regretted that cooperation has not been more general, but the work required seemed burdensome, and doubtless few could find the time to engage in it. Several of the cooperating chemists, however, have shown extraordinary industry, reporting an amount of work seldom equaled in voluntary investigation of this sort. The questions involved in the plan of work are not less than 14; hence analytical results are too complicated to admit of convenient tabulation. It seems better, therefore, to deduce from the analytical figures the answers to the several questions.

Before judging the results it is well to bear in mind the reasonable expectation of agreement or accuracy from a number of chemists working on the same subject. Last year on the simpler problem of determining nitrate-free nitrogen, the work of over 50 chemists, possibly the largest number of the association ever engaged on a single question at one time, seems to indicate that about 98 per cent of the truth is the average with present methods and present personnel. Then in the more difficult question of nitrates and the separation of several forms of nitrogen, this expectation would seem to be at least high enough. Thus methods for nitrates that give as much as 98 per cent of theory are at least as accurate as the average results on nitrate-free substance. While this limit may easily be exceeded by experienced and skillful individual analysts, it is useless to deny that it is not exceeded by the average results.

The analysts used chiefly as their source of nitrate nitrogen amounts of their own standardized nitric acid containing from 28 to 160 mgs of nitrogen. The results obtained are reported as percentages, the basis of which is the amount of nitrogen that should have been obtained.

The questions involved follow, with the answers deduced from the figures of the several analysts.

Percentages of nitrogen recorded based on amount present, using different methods. [Is nitric acid, in the absence of organic matter, reduced to ammonia without loss?]

a Analytical work reported by F. W. Rudnick throughout the report was done by F. Fenger, K. J. Monrad, and A. C. Johnson.

Percentages of nitrogen recorded based on amount present, using different methods-Cont'd. (3) BY METHOD (G).

[Distilled off magnesia followed by soda, the sum of both distillates being used.]

[Is nitric acid reduced to ammonia without loss in the presence of 1.4 to 2 grams of sugar?]

Bailey.

Morrison.

Robb..

Robertson.
Rudnick.
Robertson a

Bailey.

Morrison

Robb.

Robertson.

Rudnick

Robertson a

Bailey.
Morrison.
Rudnick.

[Distilled off magnesia followed by soda, the sum of both distillates being used.]

Bailey.
Morrison.

(8) BY METHOD (H).

[Is the sum of nitrogen in nitric acid and nitrogenous organic matter fully recovered as ammonia?]

a In the presence of 1 gram of a nitrate-free mixed fertilizer instead of sugar.

b In these determinations by the Ulsch method, the small quantity of water undoubtedly caused spurting

of alkali sufficient to drive it over into the condenser. The bumping was terrific. Rudnick.

Percentages of nitrogen recorded based on amount present, using different methods-Cont'd.

[Is any of the nitrogen in nitrate-free and ammonia-free nitrogenous bodies obtained?] (11) BY METHOD (G),a

Bailey.
Morrison.

22

1.9-2.4
2.4-3.5

2.2 3.0

a These figures were obtained distilling with magnesia only. Soda being added and distillation continued, the following additional percentages were obtained: Bailey, 8.3 to 9.3, average 8.8; Morrison, 8.3 to 11, average 9.7. These four determinations were made on cotton-seed meal containing 0.0739 gram of nitrogen, on which nitrogen the percentages are based.

(12) BY METHOD (F).

Bailey and Morrison, who alone worked on this question, report that distillation was rendered impossible by excessive frothing.

[How complete is the liberation of ammonia when distilled with magnesia?]

a These figures represent the fraction of total ammonia liberated by magnesia, the complement lacking to make 100 per cent having been liberated by soda. Thus, Cooke's lowest result was 19 per cent distilled from magnesia and the remaining 18 per cent was obtained by adding soda solution and continuing the distillation. Trescot, reported below, recovered practically all of the ammonia by magnesia alone.

(14) Is the loss of nitrogen by methods (c) and (d) caused by heat generated in mixing the acid and water?

Rudnick, using potassium nitrate instead of a solution of nitric acid, obtained the following figures, and as compared with these results those found with the solution of nitric acid by the same methods averaged 79.8 to 66.1 per cent. Trescot obtained 80 per cent when using nitric acid, as compared with 100 per cent with potassium nitrate.