6Further Gewerbe Ztg., 1868, 63; Zeit. f. anal. Chem., 8, 514. 7 Op. cit., note 3, p. 949 of this work.

Determination of water-insoluble organic matter. - Bensemann.1 - Two grams of the substance are covered with cold water and allowed to stand twelve hours, with occasional stirring. The insoluble residue is collected, washed cold, dried at 100° C, weighed, incinerated, and weighed again. Difference= weight of water-insoluble organic matter.

Determination of gum. - Boussingault.2 - An aqueous infusion of the fat-free material is precipitated with alcohol.

Determination of nitrogen. - Mansfeld3 used Kjeldahl's method, starting with 3 grams of material.

Determination of coloring matter and tannin. - Mansfeld.3 - The residue from the fat determination (see page 951) is extracted with 80 per cent alcohol. In this extract sugar, theobromine, and total residue are determined. Total residue - (sugar + theobromine) = coloring matter and tannin.

Detection of the use of fixed alkalis and ammonia in the process of manufacture of cocoas. - Stutzer.4 - The total ash, ash soluble in water, total P2O5 and P2O5 soluble in water are determined. The relative proportions of these constituents in the ash of a normal cocoa and in the ash of cocoas treated with fixed alkalis and ammonia are given in the table on page 943. Additional evidence of the use of ammonia is obtained by distillation of the sample with magnesia and determination of the ammonia in the distillate. If this process yields more than 0.1 per cent of nitrogen in the form of ammonia, this writer considers the result certain evidence of the use of ammonia, or ammonia salts, in the process of manufacture.

Methods By Which The Results Given In The Table On Page

The methods outlined below were chosen as best suited for the purpose. While some are only approximate methods, they are sufficiently accurate for the purpose and are much more rapid than some of the methods previously employed.

Microscopical examination. - The method used for the preparation of the sample for the microscopical examination has been outlined on page 949.

Determination of moisture, ash, and of the amount of add required to neutralize the ash from two grams of material. - Two grams of material are distributed over the bottom of a flat platinum dish and dried to constant weight at 100 to 105° C. The loss = moisture. The residue is carefully ignited in a muffle and weighed for the amount of ash. The ash is then washed into a beaker, dissolved, with gentle boiling, in N/10 H2SO4, and the excess of acid determined by titration with N/10 NaOH. Cc of N/10 H2S04 - cc of N/10 NaOH = the number given in the table on page 980 as "acid equivalent."

1 Op. cit., note 4, p. 949 of this work.

2 Op. cit., note 2, p. 941 of this work.

3 Op. cit., note 1, p. 950 of this work.

4 Op. cit., note 3, p. 939 of this work.

Determination of fat. - Three grams of the substance are placed in a 300 cc flask and covered with 200 to 250 cc of redistilled petroleum ether; after standing 4 to 5 hours with occasional shaking, the flask is filled nearly to the mark with petroleum ether, shaken, and allowed to stand over night. After making up to the mark and thorough shaking, the insoluble portion is allowed to deposit; the supernatant liquid is then quickly decanted into a 100 cc flask until the latter is just filled to the mark, using every precaution to avoid raising the temperature of either flask. This portion of 100 cc is filtered through a Gooch crucible, and the slight residue washed with petroleum ether until free from fat. The filtrate and washings are received in a weighed flask, in which the fat is weighed, after recovering the petroleum ether by distillation and drying the residue to constant weight at 100° C. in a water oven. The fat obtained is clear, of slightly yellowish color, and undergoes appreciable oxidation only on prolonged heating under the conditions mentioned above. An ordinary air bath is usually too small for the proper heating of a vessel of the size required. Taking the density of the insoluble portion as 1.000, and ignoring the small amount of residue decanted with the 100 cc portion, the following table of corrections is applicable to the per cent of fat obtained by the above method:

Determinations of fat are very quickly made by this method, and the results are sufficiently accurate for ordinary purposes.

Determination of sugar. - A determination of the amount of sugar added in the process of manufacture is readily made, by means of the polariscope, to within one or two per cent of the truth; a closer determination is neither very easy nor very important. The gum (see page 941) gives the aqueous solution of normal cocoa a slight rotatory power, equivalent to 0.3 to 2.0 per cent of sugar in the bean in several samples tested; the presence of starch necessitates the use of cold water, of which 500 cc or more are necessary for the complete removal of the sugar from 13.024 grams of material. Considering these facts, the following method will be found satisfactory for most purposes: 13.024 grams of material are placed in a small mortar and triturated with alcohol until a smooth paste is obtained; this is transferred to a 500 cc flask, diluted with 400 to 450 cc water and shaken occasionally for three to four hours; 10 cc of a saturated solution of normal acetate of lead are added and the volume brought to 500 cc. After standing for about one hour, with occasional shaking, the solution is filtered and polarized in a 400 mm tube. The per cent of sugar is then obtained by the following formula, in which R = the polari-scopic reading, when the normal quantity for the polariscope used is 26.048 grams:

5 R x l3.024 R [ 500-(13.024- -----------------) ]

-------------------------------------- = % sucrose

A portion of the solution, as prepared for polarization, was freed from lead and tested with Fehling's solution for reducing sugar, the result being taken as an indication of the quality of the sugar used in the manufacture of the sample.