1905. J Small Quantities of Nickel in Organic Substances. 423 



as, after a short time, the nickel compound with dimethylglyoxime separates 

 out of the coloured solution as a precipitate. 



The advantages of this method over the ammonium sulphide method are : 

 (1) small traces of iron do not interfere with the final colour, nor with the 

 sharpness of the method ; (2) smaller quantities of nickel can be accurately 

 estimated ; and (3) it is easier to work in a bad light with the pink than with 

 the brown colorimetric determination. 



Dealing with the colorimetric test alone, with solutions of pure nickel 

 sulphate, the smallest quantity which gives the reaction is 1/ 1000 milligramme. 

 To detect such a small amount, the solution must be placed in the Nessler 

 tube, then the ammonia and the solution of dimethylglyoxime added, when 

 one can recognise the characteristic pink colour, and, lastly, the fluid is made 

 up to 30 c.c. ; on comparing this with distilled water, a faint but distinct 

 difference is seen. 3/1000 milligramme gives a recognisable pink colour in 

 30 c.c. of fluid. Working with 0-07 milligramme, differences of 1/1000 

 milligramme can be recognised with a little practice. This represents a 

 potential error of + or —07 per cent. 



In test analyses, serum or blood with nickel sulphate added, the experi- 

 mental error was kept as low as 2 per cent., using about 1 milligramme of 

 nickel. For example, about 30 grammes of blood were placed in a crucible 

 and 0*9 milligramme of nickel, in the form of the dissolved sulphate, was 

 added. After ashing, extracting, removing the copper and iron groups, and 

 precipitating the nickel in the form of the sesquioxide, etc., the final fluid was 

 made up to 30 c.c. ; 2 c.c. of this fluid were compared with varying quantities 

 of a solution containing 0"01 milligramme of nickel per cubic centimetre. It 

 was found that 5"9 c.c. gave a colour, which was just too pink, and 5 - 8 c.c, a 

 colour, which was not pink enough, so that the 2 c.c. contained 0"0585 

 milligramme of nickel, and the whole solution 0'88 milligramme. This 

 represents a loss of 0*02 in 0"9, or about 2 per cent. 



Electrolysis is only to be preferred when large quantities of nickel are to- 

 be measured, while the method described above is intended for the recognition 

 and measuriug of quantities of nickel not exceeding a few milligrammes. 



