Basalt and of Lava from Etna. 95 



weathering, and was removed by the atmospheric water, while 

 the imbedded crystals being better calculated to resist such action, 

 were not destroyed. The rock was compact, and the fracture 

 uneven. Small fragments heated in a small glass retort, gave 

 off water, which produced no reaction on litmus paper. The 

 loss by heating amounted to 3.95 per cent. ; but in all the ana- 

 lyses performed, the quantity of hygroscopic water amounted to 

 nearly 1.25 per cent., so that, after subtracting the last from the 

 total loss by heating, the true quantity of water which can be 

 calculated among the constituent parts of basalt is 2.70 per cent. 

 After being heated the basalt had an altered aspect : the basis 

 became reddish, and the crystals of augite which had remained 

 unchanged, had become very perceptible. The powder of fresh 

 portions of this basalt was greenish-grey, similar to powdered 

 black augite : it formed with muriatic acid, in a short time, a 

 perfectly firm jelly ; and the same result was obtained with frag- 

 ments that were heated and finely divided. 



With the magnet only an extremely small portion could be 

 detached from the coarse powder, and this was perceptible in the 

 form of a delicate covering on the edges of the magnetic bar. 

 Thin splinters, held by platinum pincers, and acted on by the 

 blowpipe, communicated a yellow tinge to the outer flame, and 

 were melted at the edges to a black obsidian-like glass. Some 

 experiments proved to me that by the application of diluted 

 muriatic acid, the basis or the gelatinizing component part is 

 fully decomposed, while the magnetic iron is hardly at all acted 

 on ; and that the augitic portion itself, by long continued action 

 of a concentrated acid, is partially dissolved. 



By means of muriatic acid of ordinary strength, the soluble 

 portion was wholly decomposed. The silica was separated from 

 the insoluble portion by boiling with a concentrated solution of 

 carbonate of soda. An attempt to accomplish this in the me- 

 chanical way afforded an unsatisfactory result. 



The course pursued in the analysis was such as is generally 

 followed in the case of combinations which are partially decom- 

 posable by acids, and which on the other hand can be only de- 

 composed into their constituent parts by fusion with alkaline 

 carbonates. 



