504 LUTTKE'S METHOD. [BOOK n. 



dati' of the German Pharmacopoeia is added 1 ; the mixture is then 

 diluted with distilled water to the volume of 1000 c.c. Instead of 

 taking exactly one-tenth of an equivalent of AgN0 3 in grammes, 

 somewhat more, say 17'5 grms., may be taken, and the exact titre 

 determined, lege artis, by means of a perfectly exact decinormal solu- 

 tion of hydrochloric acid. Except in the case of a trained chemist, 

 the simpler plan will offer least chances of error. 



2 Deci- This solution should contain 7*6 grms. of pure 



normal soiu- NH 4 CNS per litre. In order to prepare it, 8 grms. 



tion of ammo- of the pure salt (as sold) are dissolved in 1000 c.c. of 



nium suipho- W ater. This solution must next be standardised against 



the standard acid solution of AgNO 3 . 



With this object, 10 c.c. of the silver solution are measured out 

 into a beaker, and 150 to 200 c.c. of water are added. The sulpho- 

 cyanate solution is then allowed to flow from a burette into the 

 diluted silver solution, until the first appearance of a permanent 

 reddish colouration. Supposing 9*7 c.c. were required, then 970 c.c. 

 of the sulphocyanate solution would have to be diluted to 1000 c.c. 



Finally, the diluted solution is tested against the accurately 

 prepared decinormal silver solution, so as to ascertain that they 

 absolutely correspond. 



(C) The Actual Process of Analysis. 



Liittke's process includes two determinations : firstly, that of the 

 total quantity of chlorine contained in the contents of the stomach ; 

 this quantity we shall designate a : secondly, that of the chlorides 

 remaining in the incinerated residue of the contents ; this quantity 

 we shall designate b. Having made these determinations, the quan- 

 tity of the total hydrochloric acid, both free and in organic combi- 

 nation, will be deduced from the value of a - b. The stomach 

 contents are measured out in small graduated flasks of 10 c.c. capacity, 

 and, for reasons already adduced, the solid matters are not separated 

 by filtration from the liquid in which they are suspended. 



a. Deter- 10 c.c. of the thoroughly mixed (shaken) gastric 



minationof the conte nts are poured into a graduated flask of 100 c.c. 

 e ' capacity. 20 c.c. of the decinormal acid silver solution 

 are added, the whole is shaken and set aside for 10 minutes. 



In the event of the stomach contents being strongly coloured, 

 they may be decolourised by the addition of 5 to 10 drops of a 

 solution containing one part of potassium permanganate dissolved in 

 15 parts of water. 



This addition (which is rarely necessary) must only be made after 

 all the chlorine has combined with silver, otherwise the permanganate 



1 The ' Liquor ferri persulphatis ' of the British Pharmacopoeia may be substituted 

 for the German preparation. The former is a more concentrated solution of ferric 

 sulphate, having a specific gravity of 1-441, whilst the latter varies between 1-317 and 

 1-319. 



