( 345 ) 



reflecting' l)iit dull}'; the planes n and r are frcqnenlly striped parallel 

 to the /^-axis. 



The crystals are somewhat elongated along the c-axis ; tliej'donot 

 possess a decided cleavability. 



according according 



Angular values : Measured: Calcuhiteil: \o (r.-. to />.-. 



a: m =:(1Ü0):(110)=:* 60° 56' — 60° 54' 61° 0' 



a : r = (100) : (10 J) = * 29 34 - 29 35 29 40 



m : m = (110) : (TlO) = 58 4 58° 4' 58 12 58 



r : r = (101) : (TOl) = 120 54 120 52 120 50 120 40 



m:r =r(110):(i01)= 64 58 65 64 57 65 5 



Tn convergent polarised light, the two branches of a dark hyper- 

 bola are noticed on a; the axial plane is probably i)arallel to |100|. 

 Strong donble refraction and everywhere normal extinction. 



From these determinations it follows that the substance is nothing 

 else but 'pure liexacliloroethane C^Clg, studied by Bi?ooKr^, ^) in 1824 

 and later, in 1904, by Gossner -), who obtained his crystals from 

 carbon disulphide. Gossnkr finds as optical axial plane jlOOj, with b 

 as acute bisectrix; the double refraction is strong and negative, the 

 dispersion: ^)<iv. Sp. gr. of the crystals: 2,091. 



The measiu-ements of Brooke and of Gossner are placed next to 

 mine for the pnrpose of comparison; in those of Gossner, the 6- and 

 c-axis have been interchanged, but from his axial v^alues — using 

 the plan adopted here — the axial relation is readily calculated as 

 a:b:c = 1,7965 : 1 : 3,1649. 



This leaves no doubt that the two preparations are perfectly identical. 

 A chlorine-determination after Liebig's method gave 89,757o CI ; 

 calculated 89,877o Ci On account of incomplete decomposition, 

 Carius' method always gave too little CL The melting point is situated 

 at 186° C. ; the snbstance then begins to evaporate almost at once ; so 

 its triple-point-pressure can differ but little from one atmosphere. 



§ 5. It soon became evident, that the splitting into CO,, and C^Cl^ 

 needs not to be the only reaction, uidess special precautions are taken. 

 First of all it was noticed that the same solution gave C(J^-\- C^Cl 

 in one vessel, whereas in other apparatus the liquid turned yellow, 

 and free chlorine, readily detectable, was formed together with a 

 very little chloroform; in the absence of an excess of free acid y^..^^ 



1) Brooke, Ann. of Phil. 23. 864. (1824). 



~) Gossner, Zeils. f. lirysl. und Miner. 38. 151. (1*)Ü4). 



