414 Scientific Intelligence. 



sists of 900 pairs, and is one of the largest ever constructed. The 

 same result may be obtained by a Bunsen's battery of 60 pairs, as Prof. 

 Silliman, Jr., has ofien observed. The experiments of Professors Silli- 

 man and Hare extended to the melting of various refractory substances, 

 which had never before been fused.] 



10. On the Atomic Weight of Silica; by H. Kopp, (Liebig's An- 

 nalen, Ixvii, p. 356, in Chem. Gazette, July, 1849.) — The doubts en- 

 tertained respecting the atomic weight of silicon and the composition 

 of silica according to one of the three formulae SiO, SiO 2 or SiO 3 , 

 have not been solved by the views which have hitherto prevailed on 

 this subject, where in general the decision has been made to depend on 

 the circumstance, that a particular series of compounds might be most 

 simply represented, sometimes according to one, sometimes according 

 to the other formula. A peculiar mode of conceiving this subject 

 shows that, admitting the correctness of the analytical results of Pe- 

 louze, the atomic weight of silicon with H:=l is 21*3, and the formula 

 of silicic acid SiO 3 . 



Kopp has deduced this result from the difference between the boiling- 

 points of the chiorid and bromid of silicon. The possibility of de- 

 ciding the question by this means is sufficiently evident from a number 

 of determinations of the differences between the boiling-points of sev- 

 eral chlorids and bromids, in which the chlorine, on the one hand, may 

 be regarded as a substitute for the bromine in the otherwise corres- 

 ponding bromid, thereby establishing how many degrees the boiling- 

 point rises or falls when in any compound chlorine is replaced by bro- 

 mine, or vice versa bromine by chlorine: After establishing the num- 

 ber of degrees which express this difference for the substitution of each 

 atom of chlorine or bromine, it is possible, on the other hand, to con- 

 clude, from the difference between the boiling-points of a chiorid and 

 the corresponding bromid, as to the number of atoms replaced. Now 

 it results, from the comparison of the boiling-points of several bro- 

 mids and chlorids, that the substitution of 1 CI by 1 Br raises the boiling 

 point 32° Cent, of 2 CI by 2 Br 2X32=64° of 3 CI by 3 Br 3X32=96" 

 while the boiling-point falls in the same proportion when, on the con- 

 trary, bromine is replaced by chlorine. Compare, for example, the 

 boiling point of the following substances: 



Boiling-point. 



C±H*Cl Chlorethyle . . . +11°, Pierre. 



C* H 3 Ct Chloracetyle . . . -18° to - 15°, Regnault. 



PCI 3 Chiorid of phosphorus • 78°, Dumas, Pierre. 



Boiling-point found. Calculated. 



C*H*Br Bromethyle . . . 41° Pierre. 43°. 



C*H 3 Br Bromacetyle . . . Ord. temp. 14° to 17°. 



PBr 3 Bromid of phosphorus . 175°, Pierre. 174°. 



Several other comparisons enumerated by Kopp lead to the law above 

 announced respecting the change in the boiling-point in substitutions of 

 bromine and chlorine. It consequently follows, as above stated, that 

 according as the boiling-point of a bromid, on comparison with that ot 

 its corresponding chiorid, is situated at 32, 64 or 96 degrees higher 

 than in the chlorine compound, this latter must be regarded as contain- 



o 



