A CONTRIBUTION TO THE KNOWLEDGE OF ARGININ. II 



acid was present, U) strongly pressed between the filter, to 

 remove the excess of sulphuric acid, then put in a large porcelain 

 basin, and mixed with water to the consistency of paste. Some 

 caustic lime and baryta were then added, and the whole well 

 rubbed in the basin (during the operation, the basin must be 

 cooled with water), and filtered after a few hours standing. The 

 dissolved lime and baryta in the filtrate were precipitated by 

 carbonic acid. The filtrate from the insoluble carbonates was 

 evaporated to drive off the dissolved carbonic acid, which 

 dissolves some calcium and barium carbonate, and after 24 

 hours standing, filtered. The filtrate was neutralized with a 

 known quantity of sulphuric acid and further evaporated to a 

 small volume. After cooling, the sulphuric acid, formerly 

 added, was precipitated with a calculated quantity of baryta 

 water, and the insoluble barium sulphate filtered off (during 

 the filtration, the vessels were well covered to prevent the 

 absorption of carbonic acid by the bases). The clear filtrate 

 which contains free bases, was treated according to S. G. Hedin's 

 method, with a concentrated silver nitrate solution, by which 

 some white flocculent precipitate was formed. This was removed 

 by filtration, and the clear filtrate was evaporated on the water 

 bath to a small volume, filtered once more, and left standing in* 

 a dessicator. After a short time, fine crystals of arginin silver 

 nitrate was formed, which increased very much after two or 

 three days. The crystals were then separated from the mother 

 liquor, well washed with cold water, and recrystallized from a 

 hot water solution. The crystals thus obtained were dried over 

 sulphuric acid and the percentage of silver was determined by 

 direct ignition : — 



0.083 g. crystals yielded by ignition 0.026 g. Ag = 31.3%^ 

 Calculated as C 6 H H NA, AgN0 3 +£H 2 0 &g = 30.$g% 



A portion of the crystals was dissolved in hot water and, 

 after the precipitation of silver by hydrogen sulphide, evaporated 



(1) As it is very difficult to remove hydrochloric acid by simple washing, the precipi- 

 tate was once more mixed with a large quantity of $% sulphuric acid, well rubbed in a 

 mortar, and then collected on a filter and well washed with 5% sulphuric acid. In this 

 way all traces of hydrochloric acid was removed. 



(2) As a small quantity of silver is reduced during the crystalization, it was very 

 difficult to prepare absolutely pure crystals. 



