Prof. B. Silliman i Jr., on Gibbsite and Allophane. 



413 



peated doses of fresh acid. Concentrated sulphuric acid dissolves 

 it with great energy. If the pulverized mineral is made into a 

 paste with Nordhausen acid and the temperature be slightly raised, 

 the action is so violent as to completely decompose the mineral 

 in an instant, converting the whole into a solid mass with an ev- 

 olution of great heat. This mass is perfectly soluble in water 

 save a few milligrammes of silica and hydrous oxyd of iron me- 

 chanically present. Tt is evident therefore, that either sulphuric 

 acid or the caustic alkalies must be used in attacking this mineral. 



Water. — The water of the mineral was determined on three 

 portions, selected from the purest specimens — the powdered min- 

 eral was dried at 212°, cooled over sulphuric acid, and ignited in 

 a covered platinum crucible until a constant weight was obtained. 

 The three trials gave successively 



35 206— 33-828— 33-420. Mean 34-151 pr. ct. which is a 

 little too low for the formula. 



1st Analysis. — My first analysis of this mineral was made by 

 the ordinary course of inorganic analysis without recourse to any 

 special means for the separation of phosphoric acid. 



1565 grammes substance was dissolved in concentrated sul- 

 phuric acid, evaporated to dryness, and redissolved in water. 

 The insoluble matter (silica and peroxyd of iron) weighed -0278 



. . . 



Al 



993 gramme. The filtrate from the alumina yielded 



gramme. TJ 

 and weighed 



on concentration and treatment with phosphate of soda, a small 

 quantity of magnesia, weighing "0047 gramme. No lime was pres- 

 ent. The results of this analysis yield the following summary. 



Alumina, 



Water, 



Magnesia, 

 Insoluble residue, 



9930 



5395* 



0047 



0278 



1-5650 



Found. 



63-446 



34-477 



•300 



1-777 



100-000 



Al 

 H 



lat 

 3 « 



642-33 

 33741 



979-77 



Calculated 

 65*50 



34-44 



1U0-00 



* * • 



This analysis requires therefore, the formula Al H 3 . If the 

 magnesia and insoluble matter are regarded as displacing so much 

 alumina, the requirements of the formula will be exactly met, i. e., 

 63-446 + 2070-65-5:23. 



* By the difference 



