METHOD OF LASNE 269 



operation are illustrated by the accompanying Figure 12. The first 

 receiving flask (B) contains two and one-half grams of caustic 

 soda in 25 cubic centimeters, and the second (C) a half a gram 

 in the same volume of water. The second flask is connected 

 with the aspirator, by means of which the current of air is drawn 

 through the whole apparatus. At the beginning of the operation 

 the current of dry air is drawn through slowly and the flask (A) 

 is moderately heated until its contents are brought to near the 

 boiling point. During the heating the flask should be frequently 

 shaken to secure the even distribution of the heat throughout 

 the mass, and avoid danger of breakage. In this condition the 

 evolution of the fluorin is terminated in about three hours. A 

 blank experiment should show that the sulfuric acid and sand 

 employed are free of fluorin. Sulfuric acid and sand entirely 

 free from fluorin may be easily secured by heating one liter of 

 the acid for two or three hours with 100 grams of finely ground 

 sand, previously washed with hydrochloric acid. After cooling, 

 the acid is decanted into a dry glass-stoppered flask, and the 

 residual sand is washed and dried. These reagents are, when 

 prepared in this way, both free from fluorin. When the fluorid 

 of silica is entirely evolved from the mixture, which is easily 

 determined by observing that the contents of the flask become 

 limpid, the lamp is extinguished and the mass is allowed to cool 

 until the flask can be easily handled. It is then removed and the 

 delivery tube washed into a dish into which subsequently are 

 poured the contents of the two receiving flasks, and their con- 

 necting tubes are washed with water. The solution obtained in 

 this way should still be freely alkaline, as indicated by forming 

 a red color with phenolphthalein. If it be not alkaline, a suffi- 

 cient quantity of caustic soda should be added. The contents of 

 the dish are heated for half an hour to 100 for the purpose of 

 decomposing into hydrofluoric acid and silica the fluosilicate 

 which has been formed at first. The total volume of the solution, 

 in order to facilitate the operation, should be reduced by evap- 

 oration to about 100 cubic centimeters. After partial cooling the 

 solution is saturated with carbon dioxid, the flask being covered 

 meanwhile to prevent any loss by the projection of the liquor 

 with the escaping gas. The residual liquor and the wash water 



