BY J. M. PETRIE AND H. G. CHAPMAN. .'305 



Hipeptide isolated by Levene aud Beatty*. Corroboration was 

 tlius obtained of the difficulty in completing the hydrolysis of 

 certain proteins, as noted by Osborne, Leavenworth, and 

 Brautlecht. 



Separation of hexone bases by phosphotungstic acid. — The filtered 

 digest was diluted to contain 5 % sulphuric acid. Phosphotung- 

 stic acid was added until the 5 litres contained about 5 % reagent. 

 The precipitate that fell, on the further addition of phospho- 

 tungstic acid, consisted only of reagent. After standing 72 hours 

 the superfluid was decanted, and the remaining portion separated 

 in the centrifuge. All the separations, with the subsequent 

 washing of precipitates, have been done in the centrifuge. Much 

 labour and time are saved in this way. Many precipitates are 

 driven down hard by 10 minutes' spinning, so that the superfluid 

 can he poured off. Three or four washings then suffice, as the 

 hard, practically dry mass can be suspended in water and 

 thoroughly mixed or heated as required. The solid matter is 

 again separated in the centrifuge. 



Separation of arginin fromhistidin. — The separation of arginin 

 from histidin was, in our hands, difficult. This was probably due 

 to inexperience, as an improvement was noted in each subsequent 

 hydrolysis. It was invariably found that much arginin was 

 precipitated with tlie histidin in the second silver precipitation 

 of Kossel and Kutscher. This was obvious upon applying Kossel 

 and Patten's process to the histidin portion. Nitrogen deter- 

 minations showed the presence of a quantity of arginin in the 

 filtrate from mercuric sulphate. Further, it seemed that the 

 mercuric sulphate did not completely precipitate histidin, as 

 frequently four or five precipitates containing histidin separated 

 from the filtrate, if this was allowed to stand two or three weeks. 

 On employing the precipitation by mercuric suli)hateof Kossel 

 (fe Patten previous to the second silver precipitation of Kossel k 

 Kutscher, as suggested by Osborne, Leavenworth and Brautlecht, 

 no difficulty was experienced in the separation. 



• Biocheia. Zeitsch. iv., S. 299, 1907. 

 29 



