APPENDIX. 



389 



THE PREPARATION OP CERTAIN REAGENTS AND 

 LABORATORY REQUISITES. 



Acid potassium phosphate, see p. 24. 

 Acid potassium phthalate, see p. 24. 



Almtn's reagent. 4 grams, of tannic acid in 8 cc. of strong (33 per cent.) 

 acetic acid and 190 cc. of 50 per cent, alcohol. 



Alpha-naphthoL i per cent, in strong alcohol. 



A mmonium molybdate. Rub up 75 grams, of crystalline ammonium molyb- 

 date with 300 cc. of strong ammonia. When it has dissolved gradually add 

 the solution to a mixture of 900 cc. of concentrated nitric acid (sp. gr. 1-42) 

 and 400 cc. of distilled water, cooling thoroughly during the addition. Add 

 1600 cc. of distilled water and filter, if necessary. 



Ammonium oxalate, 0-2 N. 1-42 per cent, of (COO.NH 4 ) 2 H 2 O. 



A mmonium sulphate, saturated solution. Boil 800 grams, of pure crystal- 

 line (NH 4 ) 2 SO 4 with about i litre of distilled water. Filter when cold. 



A mmonium sulphide is usually purchased. Can be prepared by saturating 

 ammonia (i part of concentrated to 2 parts of water) with sulphuretted 

 hydrogen and then adding to this one-third of its volume of ammonia of 

 the same dilution. 



Asbestos pulp for Gooch crucibles, etc. Cut some long-fibred, soft 

 asbestos into pieces about a quarter of an inch long and digest with concen- 

 trated hydrochloric acid in a large flask in a water bath for an hour, shaking 

 thoroughly at intervals. Filter through a plate or on a Buchner under light 

 suction and wash thoroughly with water. Transfer to a large wide-neck 

 stoppered bottle and shake thoroughly with water. A good quality asbestos 

 forms a sludge, which allows of rapid filtration, provided that it be not unduly 

 compressed by too great a suction. 



To prepare a Gooch crucible for gravimetric analysis, set up the apparatus 

 shewn on p. 279. Pour on enough of the asbestos sludge to form a layer 

 i to 2 mm. thick. On this place a perforated porcelain plate, the diameter 

 of which is slightly less than that of the crucible, and then add another layer 

 of asbestos. Filter under light pressure and pass water through until the 

 filtrate is absolutely clear. The crucible can then be dried in a hot air oven 

 at 1 10 C., cooled and weighed. The drying and weighing should be repeated 

 until the weight is constant. It should then be tested by passing about 500 cc. 

 of water through it, drying and weighing. If constant it is ready for use. 

 The same crucible can be used for a large number of determinations. 



Barfoed's reagent, see p. 108. 



Barium chloride, N. 122 grams, of BaCLj^HgO to i litre. 



Baryta mixture. One vol. of barium chloride solution is added two vols. 

 of baryta water. 



Baryta water. One part of crystalline barium hydroxide is dissolved in 

 15 parts of boiling water and filtered hot. The filtrate on cooling throws 

 down crystals of barium hydroxide. The supernatant fluid is baryta water. It 

 is about 0-25 Normal. 



Benedict's solution, qualitative, seep. 107. 

 Benedict's solution, quantitative, see p. 127. 



