332 Chemical Society. 



formed by evaporating solutions of carbonate of lime, he states was 

 = 2-836. 



"Specific gravity of Iceland spar is 2*72. I should suppose then that 

 there can be little doubt but that the specimen affords an example 

 of the formation of arragonite, and a verification of G. Rose's expe- 

 riments. 



" I have since made two attempts at producing arragonite by Rose's 

 method of precipitation, but cannot boast of my success. The fol- 

 lowing is a note of the best experiment. A solution of 300 grains 

 of chloride of calcium, in 4 ounces of water at 212°, was mixed ra- 

 pidly with a solution of 330 grains of carbonate of ammonia in 8 

 ounces of water at 180°. The mixed liquor was not alkaline. 



"The precipitate under the microscope consisted chiefly of radiating 

 spicular crystals, extremely minute, with occasional rhombohedrons. 

 The precipitate being washed, the specific gravity taken before dry- 

 ing came out = 2*751, after drying it was below 2*7. During the 

 washing a slight crackling noise was heard, and I cannot help think- 

 ing the precipitate may have been thrown down as arragonite, but 

 changed into calc-spar during the washing and drying." 



Professor Kuhlman of Lille presented specimens of Chalk hard- 

 ened by his process for the Silicification of Limestones, which con- 

 sists of immersing them in a solution of silicate of potash, expos- 

 ing to air for several days, and afterwards washing. Although the 

 chalk did not contain more than three or four per cent, of silica, 

 it was capable of scratching many cements and marbles. In a 

 similar manner he could harden carbonate of lead and plaster of 

 Paris. He finds alkaline salts in all the limestones containing silica, 

 which are hydraulic, and believes that they originally resembled 

 ordinary chalk in purity, but have been partially silicified by infil- 

 tration of water containing an alkaline silicate in solution, or by a 

 natural process analogous to his artificial one. 



Extract of a letter from Dr. R. F. Marchand of Berlin, " On the 

 Atomic Weight of Carbon." 



" I take this opportunity of communicating the results of experi- 

 ments relative to the atomic weight of carbon, which Professor Erd- 

 man and myself have very lately obtained. The difference between 

 the numbers recently given by Dumas and that of Berzelius was a 

 sufficient inducement for us to examine and repeat Dumas's experi- 

 ments, much occupied as we are with organic analysis. The burn- 

 ing of diamonds in oxygen gas was easily effected by us in a porce- 

 lain tube, by a pretty high temperature. The apparatus employed 

 was very similar to that described by Dumas. 



" The following are the results : — 

 No. 1. 0*8062 gramme diamonds left a residue weighing 0*0010 

 gramme, and gave 2*9467 grs. carbonic acid, consequently 

 giving the atomic weight for carbon 75*19. 

 No. 2. 1*0867 gr. left a residue weighing 0*0009 gr., and gave 



3*9875 grs. carbonic acid = carbon 74*84. 

 No. 3. 1*3575 gr. left a residue weighing 0*0018 gr., and gave 

 "4*9659 grs. carbonic acid = carbon 75*10. 



