Mustard oil can be assayed by weighing it as thiosinamine, or better by double decomposition with ammoniacal silver nitrate solution. In this case also thiosinamine is first obtained as intermediate product but, as soon as formed, it is decomposed with the precipitation of silver sulphide. According to the second method distinction is made between the gravimetric process and since the resulting products remain largely behind upon evaporation If the residue amounts to more than 3,5 g. an impermissible amount of carbon disulphide is very likely present, especially if it has the odor of ammonium sulphide.

(weighing of the precipitated silver sulphide) and the titrimetric N process (in which n/10 silver nitrate solution is used and the excess of silver nitrate is titrated back). In actual practice the titrimetric method is used well nigh exclusively. For the sake of completeness, however, the other two methods are also described.

Thiosinamine method.1) If in a flask 3 g. of mustard oil and 3 g. of alcohol are shaken together with 6 g. of ammonia water the mixture becomes clear after standing several hours in the cold (quickly at 50°) and as a rule separates crystals of thiosinamine without coloration. The mother liquid having been separated from the crystals is evaporated in such a manner that only a part thereof is transferred to the evaporating dish on a water bath and new portions added only then when the odor of ammonia has disappeared. Finally the crystals are also transferred to the evaporating dish the last traces being transferred with the aid of a little alcohol. The dish is heated on the water bath until of constant weight. The 3,25 or at most 3,5 g. of thiosinamine (corresponding to from 92,6 to 100% of Isothiocyan allyl) thus obtained constitute an brownish crystalline mass melting at 70° with a leek-like but by no means penetrating odor. It dissolves in 2 parts of warm water to a solution that does not change blue litmus paper, and possesses a bitter but not persistent taste.

It should be remembered, however, that any carbon disulphide present is likewise determined as thiosinamine, since with ammonia it undergoes the following reaction:

CS2 + 4NH8 = (NH4)SCN + (NH4)2S Carbon disulphide Ammonia Ammonium thiocyanate Ammonium sulphide of nitric acid (d15o 1,153) and a few drops of ferric ammonium sulphate are added and titrated with ammonium thiocyanate until the red color remains permanent. In order to ascertain the total amount of silver solution that has entered into the reaction, the number of cc. of ammonium thiocyanate solution used should be multiplied by 2 and the product subtracted from 50. If s grams of the alcoholic solution of mustard oil have required a cc. of

1) Direction according to the German Pharmacopoeia, 3rd ed. 1890.

The percentage of isothiocyan allyl can be computed with the aid of the formula: a .85,34 / s in which a represents the amount of thiosinamine obtained and s the amount in grams of mustard oil used.

Kremel1) has suggested the use of ammonia of definite strength and to titrate back with half-normal hydrochloric acid the amount not used. No results of practical experience with this method appear to have been recorded.

Determination with ammoniacal silver solution.

a) Titrimetric method. To about 5 g. (accurately weighed) of a solution of 1 g. mustard oil in 49 g. alcohol and contained in a 100 cc. measuring flask, 50 cc. of N/10 silver nitrate solution and 10 cc. ammonia water (d15o0,960) are added; the flask, provided with a tube 1 meter long that serves as reflux condenser, and the mixture heated for 1 hour on a water bath that is in active ebullition. After the temperature of the mixture has been reduced to that of the room, water is added to the 100 cc. mark, the contents shaken and filtered. To 50 cc. of the filtrate 6 cc.

N/10 silver nitrate solution the percentage of isothiocyan allyl in the oil is a-24,78 / s

1) Pharm. Post 21 (1888), 828.

The reactions that take place can be represented by the following equations. First of all, the ammonia acts with the formation of thiosinamine:

Ammoniacal silver nitrate breaks up this compound into allyl-cynamide aud sulphuretted hydrogen:

The sulphuretted hydrogen combines with the silver oxide to form silver sulphide.

The end reactions can be represented by the following empirical equation:

CSNC3H5 + 3NH3 + 2 AgNO3 = Ag2S + CNNHC3H5 + 2NH4NO3..

The principle of this method dates back to E. Dieterich1) who, however, suggested that the silver sulphide be weighed (see below). Gadamer2) then modified the method by making it titrimetric. Following the directions of E. Dieterich the mixture was not heated but set aside for 24 hours. K. Djeterich3) as well as Firbas4) pointed out that the decomposition of the thiosinamine with silver nitrate is not complete even after 24 hours at room temperature and that accurate values are received only then when the mixture is heated for a short time after the period of standing. Kuntze5) determined somewhat later that at room temperature more or less of the silver compound of allylsulpho-carbaminic acid ethylester is formed as well as silver sulphide. For every molecule of mustard oil this demands but one atom of silver, whereas the formation of silver sulphide demands two atoms of silver. The result is that less silver nitrate solution is used than is necessary for the complete decomposition, hence the results are too low.

1) Helfenberger Annalen 18S6, 59.

2) Arch, der Pharm. 237 (1899), 110. Comp. also Arch, der Pharm. 246 (1908), 59, footnote 2.

3) Pharm. Ztg. 45 (1900), 768.

4) Zeitschr. d. allg. osterr. Apoth. Ver. 58 (1904), 222.

5) Arch, der Pharm. 246 (1908), 58.

The precipitation of thiourethane silver is avoided if the process is carried out at higher temperature. According to Kuntze the best results are obtained if the process is carried out as described above with the exception, however, that the mixture is immediately heated on a water bath for 1 hour. According to experiments made by Kuntze, the reduction of the silver solution when boiled with alcohol need not be feared.

b) Gravimetric method. As already pointed out, the method of determining the amount of Isothiocyanallyl by means of ammoniacal silver solution was first suggested by E. Dieterich

(foe. cit.J, who, however, weighed the precipitated silver sulphide.

Somewhat later K. Dieterich1) modified the method somewhat.

One proceeds, first of all, as in the titrimetric method, but naturally it is not necessary to employ a standardized silver solution.

After the precipitate has subsided, it is collected by passing the hot liquid through a filter that has previously been washed successively with ammonia, hot water, alcohol, and ether, dried and weighed. The collected precipitate is washed with hot water, the water displaced by strong alcohol and this in turn by ether.

The precipitate thus treated is dried at about 80° until of constant weight. The percentage of Isothiocyanallyl in the oil follows from the formula a- 39,995 / s in which a = the amount in grams of silver sulphide, s = the amount in grams of mustard oil used.

According to Kuntze (loc. cit.J useful results are likewise obtained according to this method if the mixture is set aside at room temperature for 24 hours. Although, as previously indicated, thiourethane silver as well as silver sulphide may result, this effects the result but little, since the molecular weights of both compounds (248 and 252) are almost the same. As already pointed out, the side reaction may cause appreciable differences when proceeding according to the titrimetric method.

1) Helfenberger Annalen 1900, 182.