PROCEEDINGS CT GEOLOGICAL SOCIETIES. 



Ib5 



to chemical analysis, and without that no result ought to be received. In- 

 deed, Sir James Hall himself confesses his deficiency in chemical know- 

 ledge. He tells us that in various experiments he got a product in glass- 

 like drops which were semi-transparent, and this clearly proves that the 

 carbonate of lime operated upon could not have been pure. Having care- 

 fully gone over these experiments, the lecturer had no hesitation in stating 

 that he considered them to be unsatisfactory. " By the lens," he says, 

 " this same surface was seen to be glazed all over, though irregularly, 

 showing here and there some air-holes. In fracture it was semi-transpa- 

 rent, more vitreous than crystalline." Last of all, he uses platinum, to 

 obviate the effect of the iron. The effect of the iron would be to act as a 

 strongly reducing agent upon the carbonic acid by the formation of car- 

 bonic oxide, and the tendency to decompose the carbonate, would, of course, 

 be facilitated by reasons which are well known to chemists. 



It appears after all that Sir James Hall obtained some results which 

 would certainly lead us to believe that, by the application of a strong red- 

 heat, carbonate of lime would acquire a crystalline structure ; but it is ex- 

 ceedingly desirable that these experiments should be repeated with all 

 possible care, that the question may be cleared up satisfactorily. JNo 

 doubt they would involve considerable expense ; but if proper care were 

 taken, and proper apparatus employed, there is no doubt that we should 

 obtain something like very decisive results. The Hall experiments extended 

 over several years ; but, looking at the results, he could not feel that confi- 

 dence which seems to be generally reposed in them. Some years ago, 

 G-ustave Rose took up the subject, and came to the conclusion that Sir 

 James Hall had been entirely mistaken ; but more recently he has come 

 to an opposite conclusion. But Rose's experiments are by no means so 

 conclusive as they might be. In his recent experiments, which are pub- 

 lished only this year, and will be found in the 118th volume of Poggen- 

 dorf's Annalen, by employing a wrought-iron vessel, electro-plated with 

 nickel, and capable of being closed, — so avoiding the contact of iron at a 

 high temperature with the carbonate of lime operated upon, and, conse- 

 quently, the reducing action of that metal on the carbonic acid of the car- 

 bonate of line, — he succeeded in changing arragonite into a substance 

 having the characteristic appearance of Carrara marble. The experiment, 

 he tells us, was conducted in a Siemen's gas-furnace — that is, a furnace 

 capable of sustaining a long-continued and high temperature. A closed, 

 unglazed porcelain vessel was employed, and exposed to a white heat 

 during half an hour ; and he informs us that under these conditions a piece 

 of lithographic stone became greyish-white in fracture, and, under a lens, 

 was found to be finely granular. The product was analysed, and con- 

 tained — lime, 56'61 ; magnesia, 0'41 ; carbonic acid, 42*37 ; residue, 045. 

 Pure carbonate of lime contains 56 per cent, of lime and 44 per cent, of 

 carbonic acid : what was the undetermined residue ? The presence of a 

 small amount of silica might make a considerable alteration in the result. 

 After carefully examining the way in which Rose's experiment was con- 

 ducted, it appears to me inconclusive. It is obvious that there could have 

 been no sensible degree of pressure. The porcelain vessel was not in the 

 least injured, so that the temperature must have been much below that 

 which we can now command — as, for instance, in the fusion of platinum. 

 It is most desirable that we should have some further investigation on the 

 subject. The British Association might take up the question with advan- 

 tage ; they have funds at their command, and it would be exceedingly de- 

 sirable to settle this important point once for all. 



VOL. VII. 2 B 



