1905.] Small Quantities of Nickel in Organic Substances. 421 



chloric acid is added. For this purpose, 2 c.c. of a four times normal acid 

 are generally employed. The extract is then filtered. The ash so obtained 

 is practically completely soluble. 



Ashing by Kjeldahl's method, or better, with sulphuric and nitric acids, 

 can also be employed, but has two disadvantages over the simple incineration 

 method : Firstly, it takes longer ; and secondly, it introduces foreign salts, 

 which should, if possible, be avoided. 



2. Separation. — Firstly, it is necessary to get rid of the iron and at the 

 same time of the phosphates. Those tissues, which contain iron in excess, 

 e.g., blood, may be treated by precipitation with excess of ammonia and 

 filtration. The process should be repeated three times, the precipitate being 

 redissolved each time with the same quantity of acid as was used for the 

 extraction. If some of the iron separates out from the filtrate on being 

 evaporated, it may be necessary to refilter before dryness is reached. When 

 the substance contains little or no iron, it is necessary to add a sufficiency 

 to combine with the quantity of phosphates present. If the phosphates are 

 present in excess, the following method is employed. The cold solution 

 is made neutral to litmus or very faintly acid with ammonia. An excess 

 of ammonium acetate is then added (as a rule 8 to 10 c.c. of a 10-per-cent. 

 solution suffices), and sufficient ferric chloride to colour the supernatant fluid 

 yellowish-red. The mixture is then boiled, when all the iron separates out 

 as phosphate and basic acetate. For those tissues yielding large quantities of 

 phosphates, e.g., liver, the amount of ferric chloride necessary is comparatively 

 large, and some difficulty may be experienced with the filtration. The only 

 possible help is obtained by using two or more filters. The washing of the 

 precipitate must be carried out carefully, in spite of the considerable loss of 

 time. Precipitation by ammonia may be carried out for the three subsequent 

 repetitions. The precipitate is each time dissolved in the smallest possible 

 quantity of acid. 



After the united filtrates have been evaporated to dryness, the residue is 

 again dissolved in water, and dilute hydrochloric acid added, about 6 c.c. of 

 four times normal acid being usually sufficient. Sulphuretted hydrogen 

 is then passed through the hot solution for at least half an hour, and it is 

 then allowed to stand for a time, as the sulphides, which form in acid solution 

 do not always readily separate out. The liquid is then filtered and the precipi- 

 tate well washed with sulphuretted hydrogen water. The filtrate is again 

 evaporated to dryness, re-dissolved in a little water on the water bath and then 

 a solution of pure sodium hydrate is added in successive portions to the hot 

 liquid, until no more ammonia comes off. Care should be taken to use 

 as little sodium hydrate solution as possible, as every sample in the market 



