Chemistry and Physics. 405 
of being a consequence of its absence in the coal itself, is really due to 
the high temperature at which the ash is formed. We have here the 
explanation of a fact which might otherwise appear inconsistent with 
the admitted vegetable origin of coal. 
(7.) Another incidental result of interest, is the extraction of carbon- 
aie of potassa from wood by leaching it in fine powder, with carbona- 
ted water. This effect we have found to be quite distinct with maple, 
oak, hickory, &c, Hitherto the opinion appears to have prevailed that 
the alkali or its carbonate could only be eliminated by the incineration 
of the vegetable material. 
rom the great rapidity with which, according to our experiments, 
potassa and soda and their carbonates, but especially potassa and its 
carbonate, rise in vapor at a strong red heat, we 
arge error must be committed in estimating the amount of these mate- 
not already been brought to the notice of analysts, as likely to modify 
materially their results. 
2. General Formulas for the Silicates and Borates; by A. Lav- 
RENT, (Compt. Rend. des Trav. de Chemie, July, 1847, from Compt. 
Rend. de |’Acad., t. xxiii, p. 1050, and t. xxiv, p. 94.)—In these me- 
moirs M. Laurent remarks upon the complication of the formulas gen- 
erally admitted in the dualistic system, and upon the difficulties of clas- 
Sification after this system. 
To avoid the numerous contradictions which render so difficult the 
Study of the native silicates, he has reduced them to a small number 
of types with the following formulas, (admitting with the French chem- 
ists generally, that the formula of silicic acid is SiO, and representing 
y 4 an equivalent of hydrogen ae metal. 
Silicates SiO+20R,]=Si O, (R,) 
Bisilicates, [28i O+20R, |=Si, O, (R,) 
Trisilicates, [38SiO+2OR, ]=Si,O, (R,) 
Quadrisilicates, 48iO+20R, |=Si, O, (R,) 
Quintisilicates, 5Si O+-2O0R, ]J=Si, O, (R,) 
Sexsilicates, .  [68i0+20R, |=Si, Og By . 
Octosil .  [SSiO+20R,]=Si, O,(R,) 
am, and OF e+ or OF e?,, = oxyd of ferricum.) He thinks that fer- 
