142 CHEMICAL STATICS 



peptids, peptones and proteins have been extensively investi- 

 gated by Kober (57) (58) (59) (60) and, more recently, by Osborne 

 and Leavenworth (88). Kober has shown that the copper salts 

 of amino-acids in alkaline solutions yield their copper quanti- 

 tatively in the form of a precipitate of cupric hydrate on heating 

 the solution or on addition of an excess of alkali. Under similar 

 conditions the peptones and peptids yield little or no precipitate. 

 Osborne and Leavenworth have shown that the maximum amount 

 of cupric hydrate which edestin or gliadin will hold in solution 

 exactly corresponds with the number of — COHN— groups in 

 the molecule of these proteins, assuming that one atom of copper 

 combines with each nitrogen atom. This fact would appear 

 to be at variance with the view expressed by Kober and Sugiura 

 (59) that the pink "biuret" color which alkaline solutions of the 

 peptone compounds of copper yield on heating is due to a union 

 of copper with four nitrogen atoms, for if this were the case the 

 development of the pink color would lead to the precipitation of 

 an excess of cupric hydrate previously held in solution by the 

 — COHN— groups of the peptone. 



Neumann (84) has studied the compounds which ovomucoid 

 forms with various metal salts (ZnCl2, CuCU, MgCU, AICI3, FeCls) 

 and finds that in alkaline solutions this protein forms insoluble 

 compounds with the heavy metal, the weight of the metal com- 

 bined being proportionate to the molecular weight of its hydrox- 

 ide. In other words, ovomucoid and the various hydroxides of 

 the heavy metals combine in stoichiometrical proportions. 



Rona and Michaelis (106) have shown that ferric hydrate will 

 displace Ca(0H)2 from its combination with casein, forming 

 insoluble ferric caseinate. Benedicenti and Rebello-Alves (15) 

 (16) have shown that the magnetic properties of iron in solution 

 or even of finely pulverized iron suspended in water are "masked" 

 by the presence of proteins. They believe that in the latter 

 case this phenomenon is attributable to a direct fixation of the 

 metallic ions by the protein. 



Henze (42) has described an interesting chromogenic protein 

 in the blood corpuscles of ascidians in which vanadium would 

 appear to play the part of the iron in the haemoglobin of mam- 

 malian corpuscles. 



2. The Compounds with the Phosphoric Acids. — It was 

 pointed out by Graham in 1861 that metaphosphoric acid unites 



