REAGENTS AND SOLUTIONS 



Alizarin. 1 A i per cent solution of alizarin mono-sodium sulphonate 

 in water. 



Almen's Reagent. 2 Dissolve 5 grams of tannic acid in 240 c.c. of 

 50 per cent alcohol and add 10 c.c. of 25 per cent acetic acid. 



Aluminium Hydroxide Cream. 3 To a i per cent solution of ammo- 

 nium alum at room temperature add a slight excess of a i per cent solu- 

 tion of ammonium hydroxide. Wash by decantation until the wash 

 water shows only the faintest trace of residue on evaporation. 



Ammoniacal Silver Solution. 4 Dissolve^26 grams of silver nitrate 

 in about 500 c.c. of water, add enough ammonium hydroxide to redis- 

 solve the precipitate which forms upon the first addition of the ammo- 

 nium hydroxide and make the volume of the mixture up to i liter with 

 water. 



Ammonium Thiocyanate Solution. 5 This solution is made of such 

 a strength that i c.c. of it is equal to i c.c. of the standard silver nitrate 

 solution mentioned below. To prepare the solution dissolve 12.9 grams 

 of ammonium thiocyanate, NH 4 SCN, in a little less than a liter of 

 water. In a small flask place 20 c.c. of the standard silver nitrate 

 solution, 5 c.c. of a cold saturated solution of ferric alum and 4 c.c. of 

 nitric acid'(sp. gr. 1.2), add water to make the total volume 100 c.c., and 

 thoroughly mix the contents of the flask. Now run in the ammonium 

 thiocyanate. solution from a burette until a permanent red-brown tinge is 

 produced. This is the end-reaction and indicates that the last trace 

 of silver nitrate has been precipitated. Take the burette reading and 

 calculate the amount of water necessary to use in diluting the ammo- 

 nium thiocyanate in order that 10 c.c. of this solution may be exactly 

 equal to 10 c.c. of the silver nitrate solution. Make the dilution and 

 titrate again to be certain that the solution is of the proper strength. 



Arnold-Lipliawsky Reagent. This reagent consists of two definite 

 solutions which are ordinarily preserved separately and mixed just before 

 using. The two solutions are prepared as follows: 



(a) One per cent aqueous solution of potassium nitrate. 



1 Indicator in various procedures, pp. 177 and 501. 



* Ott's precipitation test, p. 444. Determination of lactalbumin, p. 346. 

 3 Removal of protein in various methods, pp. 346, 506. 

 1 Purine base precipitant, p. 129. 



6 Volhard-Arnold method, p. 572, and Volhard- Harvey method, p. 573. 



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