560 MINERALOGY 



the decomposition of silicates in testing for the potassium flame. 

 The flux should be tested for the potassium flame to insure its 

 purity. 



Von Kobell's flux. Made by mixing equal parts of potassium 

 iodide and flowers of sulphur. Used in -testing for the lead and 

 bismuth iodide coats on coal. 



Blue litmus paper. Used in testing the acidity of fumes and of 

 the water yielded in the closed tube. 



Turmeric paper. Used in the alkaline test and also for the detec- 

 tion of boric acid and zirconium. 



REAGENTS USED IN SOLUTION 



Wet reagents are made up in the strengths indicated in each 

 instance. They should be kept in bottles with tightly fitting 

 ground glass stoppers. The water used is distilled. 



Hydrochloric acid, used in two strengths. Concentrated as 

 obtained from the" supply houses is spc. 1.19 to 1.20, containing 

 about 39 per cent. HC1. The dilute acid is made by adding an 

 equal volume of water to the concentrated ; this yields a solution of 

 HC1 a little stronger than five times normal, 5 n. 



Sulphuric acid, H 2 SO 4 , the concentrated as obtained is spc. 

 1.84 and is 36 times normal. The dilute is made by pouring slowly 

 one volume of concentrated acid into six volumes of water; the 

 diluted acid will be approximately five times normal, 5 n. 



Nitric acid. The concentrated acid is spc. 1.42, and contains 

 69 per cent. HN0 3 , equal to 16 times normal. The dilute acid is 

 made by mixing 5 volumes of acid with 1 1 volumes of water ; the 

 diluted acid will be approximately 5 n. 



Acetic acid, CH 3 COOH, used in some wet tests, as in the tests 

 for chromates. 



Hydrogen sulphide, H 2 S, is generated by treating ferrous sul- 

 phide with sulphuric acid, FeS + H 2 SO 4 = FeSO 4 + H 2 S. A 

 bottle may be used as the generator ; the acid is poured in the 

 thistle tube or funnel, the lower end of which extends to the bottom 

 of the bottle. The H 2 S gas generator is led off through the bent 

 tube. It is either used as a gas or absorbed in water. The water 

 solution is kept in a bottle, thus avoiding the use of the generator 

 in each test. 



Sodium hydroxide, NaOH, 200 gm. of the sticks are dissolved in 

 water and diluted to a liter. The solution will be 5 n. One cc. of 



