Proceedings of tee Polytechnic Association. 843 



Crystals in Diamonds. 

 Mr, Sorby has proved that what were supposed by the late Sir 

 David Brewster to be cavities in diamonds, are in reality crystals, 

 and tliat the tine lines or cracks radiating from these crystals are the 

 result of contraction. The same phenomena are seen when a fused 

 globule of borax glass inclosing a crystal is allowed to cool slowly. 

 This view leads us to the conclusion that such, and perhaps all, dia- 

 monds are formed at a high temperature. 



Preservation of Hydriodio Acid. 

 This acid will be preserved in a white state by the presence of 

 turnings of copper. The iodide of copper, which is very slowly 

 formed, is not dissolved by the acid. 



Aqua Kegia and Metallic SuLPniDES. 

 Mr. Lefort finds that when acpia regia is placed in contact with 

 sulphur, or with metallic ores containing sulphur, chloride of sulphur 

 is first formed by the decomposition of the liydrochloric acid, but 

 soon after the first compound is destroyed by the nitric acid, and 

 chlorine gas is set free, while sulphuric acid is formed. The best 

 proportions of 'the mixed acids for securing rapid decomposition of 

 the sulphides is one part of hydrochloric acid with three parts of 

 nitric acid ; the reverse of these is ordinary aqua regia, which con- 

 sists of three parts of hydrochloric and one of nitric acid. 



Chemical Action Arrested by Pressure. 



Mr. Cailletet has found that the strongest acids properly mixed 

 with water cease to disengage hydrogen in the presence of iron, tin, 

 zinc, aluminum or sulphureted hydrogen when in contact with sul- 

 phide of iron, provided a. strong pressure is exerted within the retort 

 containing these substances. 



Mr. Phin, — It is my impression Mr. Chairman, that Mr. Cailletet 

 has deceived himself in this case. I have frequently prepared hydro- 

 gen by the action of acid on zinc under comparatively strong press- 

 ure, say ten atmospheres ; but the pressures employed by me were 

 very low, when compared with those employed by an experimenter 

 who reported the results of his investigations in one of the early vol- 

 umes of the reports of the British Association for the Advancement 

 of Science. He used zinc and sulphuric acid, and the pressures 

 attained were very high ; as high as he could get iron vessels to with- 



