318 Guibourt on Arsenic, 



arsenic and its compounds ; and has succeeded in explaining so 

 far some of the anomalies and discrepancies which the investiga- 

 tions of previous experimenters have presented. 



According to Bergmann, the specific gravity of metallic arse- 

 nic, when melted, is 8.308, but in its native state only 5.763. M. 

 Guibourt found, that small portions of the latter had a specific 

 gravity of 5.789 ; but larger fragments, in consequence of the 

 interstices between the conglomerated crystals, did not exceed 

 4.166. He failed in several attempts to fuse it under pressure, 

 and was deterred from repeating them by a formidable explosion. 

 But he found the weight of several fragments, which were agglu- 

 tinated by heat, to be 5.959- 



The oxide of arsenic, though it has been examined by many 

 able chemists, still presents some obscurities in regard both to 

 its physical and its chemical properties. Guibourt has found, 

 that the discrepancies among former experimenters may be partly 

 reconciled by a difference in property which exists between the 

 oxide in its transparent, fresh-prepared state, and in that more 

 common opaque form, which it assumes after being long kept. 

 Transparent specimens, he finds, have a specific gravity of 

 3.7385 ; the opaque varieties are somewhat lighter, being 3.695. 

 He has never been able to observe any specimen with the high 

 specific gravity of 5.0 assigned by Bergmann. His results agree 

 with those of our countryman Dr Ure, who found the specific 

 gravity to vary from 3.728 to 3.730. Very opposite statements 

 have been made with respect to its solubility. The most accu- 

 rate, however, have been generally considered to be those of 

 Klaproth ; who found that a hundred parts of water dissolve a 

 quarter of a part at a mean temperature, 7.77 parts at the boil- 

 ing temperature, and retain 3 of these on cooling. Guibourt finds, 

 that the transparent oxide is less soluble than the opaque va- 

 riety. Of the former 100 parts of temperate water dissolve 

 nearly one part ; and 100 parts of boiling water take up 9.68 

 parts, and retain If on cooling. Of the opaque variety 100 

 parts of water dissolve IJ at a mean temperature, 11.47 at the 

 boihng temperature, and retain 2.9 on cooling. Chemists are 

 as little agreed regarding the effects of its solutions on vegetable 

 colour. Guibourt has remarked, that the transparent variety 

 reddens litmus faintly, bat that the opaque variety restores its 



