410 Progress of Natural History, 



tuted Prussian blue for indigo in dying silk, thread, and cotton. 

 M. Raymond the younger has improved on his father's pro- 

 cess by imparting the same colour to woollen materials. The 

 dye thus given is brighter than that from indigo, remains un- 

 injured by vv^ater, fresh air, and light, but changes imme- 

 diately when it comes in contact with boiling soap-suds and 

 alkaline liquids. 



M. Chevreul, so long known for his experiments on greasy 

 substances, has been enabled to extract the greasy matter 

 contained in wool, by the action of alcohol and ether. In 

 this state wool is more difficult to dye, but if dipped into sub- 

 carbonate of soda, it regains its power of absorbing colouring 

 matters. 



MM. Chevalier and Lenglum^ have been of essential 

 service to the art of lithography, by the composition of two 

 substances : the one for preparing the stone to receive the 

 drawing, and printing from it when drawn upon, and the other 

 for effacing the drawing. The first is an acid, which renders 

 the surface of the stone more capable of imbibing the water 

 which resists the printing-ink, and abstracts every thing 

 like alkali from the material used for drawing. The receipt 

 is as follows : — 3lbs. of hydro-chloric acid mixed with 

 white marble. Filter the solution, and add 3 lbs. of water. 

 Then melt 12oz. of gum arabic in this mixture; and lastly 

 add 3 oz. more of hydro-chloric acid, which can be in- 

 creased if more strength be required. This liquid spreads 

 itself more equally over the stone, and preserves humidity 

 longer than any other yet in use. The second substance 

 spoken of above, is potash, rendered caustic by lime, and dis- 

 solved in sixteen parts of water. The stone is washed, and 

 then left in this liquid for four hours, which operation is re- 

 peated, as often as necessary, upon the whole or part of the 

 stone. This, by entirely taking out the drawing, supersedes 

 the use of pumice, sandstone, &c., which in time wear away 

 the stone. 



M. Beudant, who has long devoted himself to the relative 

 weights and proportions of minerals, has ascertained that the 

 specific gravity of these bodies is not as uniform as hitherto 

 supposed. Carbonated lime, for instance, varies between 2*7 

 and 2-5 ; arragonite between 2*9 and 2*7. The state of crys- 

 tallisation has a sensible influence over these variations. The 

 specific gravity of small crystals is the greatest, and it probably 

 diminishes in larger crystals from their internal vacuities being 

 greater than in a more homogeneous mass. The varieties of 

 lamellar, or fibrous structure, are also the lightest, and decrease 

 still further in weight as the fibres increase in size. The spe^ 



