OF ARTS AND SCIENCES. 295 



adjustments of composition to take place. The subsequent solution 

 and boiling determines the precipitation of compounds not soluble in 

 the medium. This medium is subsequently decomposed and products 

 divided. 



MODE OF ANALYSIS. 



The rock perfectly cleansed by washing and brushing, reduced to fine 

 l^owder, is either dried for its combined water or taken in its natural 

 state. A flux is prepared by melting 202 parts of potassic nitrate with 

 63 parts of sodic carbonate, both pure. The cooled mass, reduced to 

 powder, absorbs about 0.004 parts when exposed to the air, and must 

 be kept in a closed bottle. This basis flux can be adapted to meet all 

 cases of varied comj)Osition in minerals. 1 grm. of the rock or mineral 

 is mixed intimately with 1.28 grm. or 2 grms. of this flux in a tall, 

 narrow crucible of platinum, on which no action is exerted. The ciu- 

 cible, covered, is heated o\'er an ordinary Bunsen table lamp, gently 

 while intumescence continues: the heat increased, hissing ceases, a 

 slow sintering follows, and in 12 to 20 minutes the action is over, 

 about one-half the whole power of the lamp being used. 



The fused mass, mostly removed fi om the crucible by a looped 

 platinum wire, with the crucible and cover are boiled in water. The 

 basic silicates, more or less altered, remain ; the soluble compounds dis- 

 solve, and the filtered solutions and washings, making 40 to 50 CC, 

 . are evaporated in a platinum basin to about 6 CC. To the hot solution, 

 amnionic chloride, a little in excess of the equivalent of sodic carbonate 

 used, is added, from a titrated pure solution, the basin put on a water- 

 bath, the contents evaporated, and carefully di'ied at temperature not 

 exceeding 100° C. After the addition of the ammonic chloride, the 

 silicic acid gelatinizes, and, in drying, passes out of combination with 

 the alkalies. By subsequent boiling in water and filtration, the pre- 

 cipitated silicic comjjounds are obtained. 



The filtrate and washings contain other combinations, which can be 

 treated either in the normal state of acid ammonic salts, or after the 

 addition of a drop of ammonic hydrate renders the solution neutral to 

 test-jxiper. Numerous cases occur, rendering modifications necessary. 

 Chlorine, bromine, iodine, sulphur, compel a choice of ammonic salts. 

 Many of the acid-forming metals are separated by their characteristic 

 reactions, from the residue of fusion. In general, if the solution of 

 the result of fusion does not deposit silicic acid on the addition of an 

 ammonic salt, 0.25 grm. of silicic acid, with or without its equivalent 

 of sodic carbonate, is added ; because the displacement of other acids 



