378 Account of some Expemnenls 



gas, after having remained in contact with the water a 

 whole night, ceased to be diminished. Accnrdinr!; to this 

 resuh, the proper correction bcine; made for the additional 

 pressure, water decomposes about 263 times its bulk of si- 

 licated fluoric acid gas. 



Dr. Priestley observed, that muriatic acid gas reproduced 

 silicated fluoric gas from the crust of silex formed, when 

 the latter is condensed by waler*. This experiment I 

 have repeated, and as it appears to show more correctly the 

 quantity of gas waler can condense, I shall describe the re- 

 sult. 2*4 cubic inches of muriatic gas were added to a 

 drop of water, that had previously absorbed one cubic inch 

 of silicated fluoric gas, in a jar over mercury. There was 

 an immediate absorption equal to yV "f ^ cubic inch. The 

 mixture of silex and subsilicated fluoric acid efiVrvesced, 

 and from an apparent solid became fluid, the whole of the 

 silex gradually disappearing. After the first-mentioned 

 absorption, there was no further. The gas produced was 

 silicated, as appeared from the crust it deposited when 

 removed to waler, aud the liquid formed was pure muria- 

 tic acid ; for, decomposed by concentrated sulphuric, it 

 afforded merely muriatic acid gas, without any silicated 

 fluoric. The evident conclusion from the preceding result 

 is, that water condenses equal quantities of the muriatic 

 and silicated fluoric acid gases, and consequently that the 

 first estimate is too low, and instead of 263 times its bulk, 

 it is probably more correct to say that water to be saturated 

 requires at least 363 times its volume. Neither will this 

 estimate appear inconsistent with the former result, when 

 the deposition of «ilex is considered as an obstacle to the 

 free exposure of the surface of the water to the £ras. 



Subsilicated fluoric acid is decomposed by ammonia and 

 the fixed alkalies, aud by all the earths that 1 have made 

 trial of. It is also decomposed by the sulphuric acid and 

 the boracic, as well as by the muriatic acid gas. 



Of the particular changes which occur when it is acted 

 upon by the arcalies, I defer giving any account at present, 

 as it is my intention to do it in the next section. 



To learn the effect of heat on it, a small quantity of 

 strong acid, pure and transparent, was introduced into a 

 retort connected wiih mercury. A spirit lamp bcinor ap- 

 plied, about three cubic inches of i^ilicaled fluoric acid gas 

 were produced. The neck of the retort was lined with si- 

 lex in a gelatinous state, and raqch liquid subsilicated 



* Vido Piiestlcy on Air, vol. ii. p. 202. 



fluorii; 



