386 Intelligence and Miscellaneous Articles, 



as I was assured by M. G. Rose. These lamellae therefore resemble 

 quartz. 



These facts show that silica is precipitated in the different states 

 I have mentioned, at the instant that the carbonic acid of the atmo- 

 spheric air which enters the flask combines with the potash holding 

 the silica in solution, and that at the same time the carbonate of 

 potash formed reacts upon and decomposes the sulphate of lime. 

 The effects produced must be attributed to this double reaction. 



Double Carbonate of Copper and Soda (NaO, CuO, 200^). — I 

 have in a previous memoir* stated that bibasic carbonate of copper, 

 (malachite) 2CuO, CO^ 2H0, may be obtained by immersing a 

 fragment of limestone covered with crystallized subnitrate of copper, 

 4CuO NO*, 3H0, into a dilute solution of bicarbonate of soda, and 

 that if the action is allowed to go on until the whole of the sub- 

 nitrate has been converted into bibasic carbonate, the latter is itself 

 decomposed with production of a double carbonate of copper and 

 soda in very minute crystals of a clear blue colour, which adhere 

 firmly to the chalk. At the time that I wrote that memoir I com- 

 menced several experiments, with the intention of leaving them to 

 spontaneous action during several months. Last November, on 

 taking the fragments of limestone covered with subnitrate of copper 

 out of the solution of bicarbonate of soda, in which they had been 

 placed six months previously, I found the bibasic carbonate for the 

 most part decomposed and converted into double carbonate of copper 

 and soda, in beautiful microscopic crystals, having the form of right 

 rhombic prisms with truncated summits. 



Bibasic Arseniate of Lime and Ammonia. — When a fragment of 

 limestone or chalk is left for some months in contact with a saturated 

 solution of arseniate of ammonia in considerable excess, after the 

 lapse of a certain time, very perfect transparent crystals are per- 

 ceived upon its surface ; in a preparation which was made at the 

 commencement of 1852, these crystals are more than a centimetre 

 on each side. Their form is an oblique rhomboidal prism. One of 

 them presents very distinct modifications at the edges, indicating a 

 double truncation, constituting a pyramid with four planes at each 

 of the bases. The crystals effloresce very rapidly in the air, losing 

 ammonia and water; the analysis, which I was unable to repeat 

 from want of material, appeared to show that they were a double 

 arseniate of lime and ammonia with a large quantity of water of 

 crystallization. 



It was to be expected that the other earthy bases — baryta, strontia, 

 magnesia, &c. — would behave in the same manner as lime in the 

 reaction of their carbonates upon arseniate of ammonia, and I there- 

 fore made some arrangements for the purpose of verifying this con- 

 jecture; after a few days I recognized upon the surface of the 

 carbonates acicular crystals which could not be other than double 

 compounds of arseniate of ammonia and the arseniates of the earthy 

 bases. When a suflicient quantity of these crystals are formed, I 

 shall analyse them in order to determine the composition of this new 

 series of compounds. 



* PhiL Mag. Ser.4. vol. iii.p. 235. 



