20 



solved in dilute hydrochloric acid, 25 grams of real HC1 to the liter. 

 Solutions of two degrees of strength were prepared, the one containing 50 

 grains of the solid reagent to the liter, the other 100 grams. In the 

 experiments with tannic acid, solutions in like manner containing 50 

 and 100 grams, respectively, of a remarkably good sample of the 

 reagent, dissolving readily to a perfectly clear liquid, were made use of. 



It has been assumed by Stutzer and others that the proteid and 

 allied substances are precipitated by phospho tungstic acid, while the 

 simpler ainids and amido acids are not so precipitated. As qualifying 

 this general assumption, it has been stated that some of the proteid 

 derivatives, as the peptones, 1 are incompletely precipitated, and on the 

 other hand that the flesh bases, kreatin, kreatinin, etc., are fully pre- 

 cipitated. The reagent in question has been recommended as the 

 means of separating and determining them. 2 



Account does not seem to have been taken hitherto of the fact that 

 some of the precipitates formed by substances of amidic character with 

 phospho-tungstic acid are to a small extent soluble in water, and that 

 their solubility is much increased by rise of temperature. 



CLASSIFICATION OF SUBSTANCES EXAMINED. 



It has been found that the various substances on which these experi- 

 ments have been made fall into three classes, as follows: 



(a) Those which, even in pretty strong solutions, give no precipitate 

 with phospho-tungstic acid. 



(&) Those which are precipitated at any rate in strong solutions, the 

 precipitate redissolving with more or less ease on heat being applied to 

 the liquid or on treating the precipitate with hot water, and reappear- 

 ing on cooling. 



(c) Those which are precipitated, the precipitate not being sensibly 

 soluble and the supernatant liquid remaining clear on being heated 

 along Avith the precipitate and subsequently cooled. 



Under the first head fall glycocin, alanin, leucin, aspartic acid, aspar- 

 agin, glutainic acid, tyrosin, and allantoin. In the case of alanin there 

 was a very slight turbidity, not increased by using a saturated solution, 

 suggesting the probability of a trace of some impurity being present. 



Under the second head were observed glutamiu, a slight precipitate, 

 the solution easily cleared by heating, the turbidity reappearing on 

 cooling; betaine in strong solution, a copious white precipitate, dis- 

 solving gradually on addition of more water and heating, the precipi- 

 tate reappearing on cooling; kreatiu, strong precipitate, solution 



] Dr, W. D. Halliburton in the article "Proteids" m Watts's Dictionary of Chem- 

 istry, revised edition, Vol. IV, p. 331. In Garugee's Text-book of Physiological 

 Chemistry, Vol. II, p. 139, it is stated that peptones are precipitated by phospho- 

 tuugstic and phospho-inolybdic acids, and that these two reagents furnish the means 

 of separating them. A similar unqualified statement is to be found in the Appendix 

 (by A. Sheridan Lea) to Michael Foster's Text-book of Physiology, p. 45. 



-Koeuig and Boeiner Zeitschrift fiiraualyt. Chemie., 34, 560, adopted in Prof. H.W. 

 Wiley's Principles and Practice of Agricultural Analysis, 3, 454. 



