CHAP. I.] QUANTITATIVE ANALYSIS OF SALIVA. 55 



Determina- A known weight (30 50 grms.) of filtered saliva is 



tion of mucin treated with a v few drops of acetic acid. Mucin is pre- 



(with epithe- cipitated; it may be collected on a weighed filter, washed 



with absolute alcohol and then with ether, and the 



combined weight of filter and mucin determined. 



Determina- All saliva contains, as has been said, some proteid 

 tion of Pro- bodies in solution. As the quantity is small and there 

 is always some, usually a preponderating quantity of 

 mucin, the determination does not admit of great accuracy. The 

 following plan is recommended, but is only applicable when con- 

 siderable quantities of saliva are available. 



To 50, or better still 100 grms. of saliva add a few drops of acetic 

 acid ; collect the precipitated mucin, following the directions given in 

 the last paragraph. To the filtrate add at least three times its volume 

 of absolute alcohol, and set aside the mixture for 24 hours. Collect 

 the precipitate on a weighed-filter, wash with absolute alcohol, and 

 ether, and then with boiling water. The filter with its contents is 

 then dried, first in the water-oven and then in the air-oven at 120C., 

 and weighed between watch-glasses. Thus we determine the com- 

 bined weight of the proteids and of certain of the salts present in the 

 portion of saliva analysed. The filter and contents are then ignited 

 in a weighed platinum capsule, and after the operation the weight of 

 the ash left is determined. On subtracting from the weight of the pro- 

 teids and ash, as found by the previous operation, the weight of the 

 ash, we obtain the weight of the proteids present. 



Determina- 



tion of the The presence of sulphocyanic acid is established 

 presence and by the tests referred to at page 19. 



w The amount of sulphocyanic acid is best deter- 



sa iiv a - mined by the following method, which was carried out 

 Munk's me- by Munk at the suggestion of Salkowski 1 : 

 thod. 



A known weight of saliva is evaporated to dry ness, and an alco- 

 holic solution of the dry residue is made ; this is evaporated to dryness, 

 dissolved in water, and the clear solution is precipitated by means of 

 silver nitrate and nitric acid ; the precipitate is washed, collected on 

 a filter, and dried at 100C. ; it is then ignited in a silver dish, with 

 pure sodium hydrate and potassium nitrate. The fused mass is dis- 

 solved in water and the solution is treated with hydrochloric acid 

 and barium chloride, which precipitates the sulphuric acid formed 

 by the oxidation of the sulphocyanic acid. From the weight of the 

 barium sulphate the amount of sulphur originally present in the 

 sulphocyanate is ascertained. 



Coiorimetri- The estimation of the amount of sulphocyanic acid 



cai methods. i n the saliva has been usually carried out by more or 



1 Munk, ' Schwefelcyanbestimmung im Speichel.' Virchow's Archiv, Vol. LXIX. 

 p. 350. 



