204 Proceedings Columbia Biochemical Association [March, 



drops each of lo percent acetic acid and lo percent potassium Chro- 

 mate sol., a heavy flocculent, yellow-brown precipitate is produced, 

 which is easily separated by iiltration.^ Excess of Chromate may 

 be removed from the clear filtrate with a few drops of lo percent 

 barium chlorid sol., after nearly neutralizing the acid with ammo- 

 nium hydroxid. When filtered through double quantitative filter 

 paper, the clear filtrate gives no response to the biuret test, thus 

 showing that precipitation of protein has been complete. Lithium, 

 calcium, Strontium and f erric Chromates, and potassium bichromate, 

 produce similar precipitates. Dilute mineral acids may be used in- 

 stead of acetic, though boric acid is altogether too weak. Too much 

 acid prevents clear filtration and too much Chromate seems to dis- 

 solve the precipitate. 



Fresh extracts of most of the tissues of the body, as kidney, 

 brain, lung, intestine, stomach, and heart give similar precipitates. 

 Fresh blood must be diluted 1-5 or i-io, and treated with the 

 proportions of 15 cc. of acid and 10 cc. of Chromate sol. per 100 

 cc. of diluted fluid, to give complete precipitation. Milk and dilute 

 egg-white give very heavy precipitates but the filtrates are not clear 

 unless the phosphates are first eliminated. Since the filtrate from 

 egg-white always contained some protein, ovomucoid was pre- 

 pared and purified in the usual way, and its precipitability tested. 

 It was not precipitated by the acid-chromate combination. 



Of derived proteins, metaproteins obtained by acid extraction 

 of meat were always completely precipitated. Amino acids, pep- 

 tones and secondary proteoses give no precipitates. Primary pro- 

 teoses, purified according to Kühne, yielded heavy yellow precipi- 

 tates, but the filtrates responded weakly to the biuret test. Pos- 

 sibly secondary proteoses were present despite the thoroughness of 

 purification. 



Of related nitrogenous products, Adams' beef extract gives no 

 precipitate, nor does an alcoholic extract of the total solids of urine. 

 Of alkaloids, atropin yields an emulsion: narcein and brucin, char- 

 acteristic crystals; narcotin, morphin, and apomorphin, dark floc- 

 culent precipitates. 



9 Gies : American Journal of Physiology, 1903, viii ; Proceedings of the 

 American Physiological Society, p. xv. 



