166 Professors Rogers on the Decomposition 



water, the result is much feebler, and requires a longer time. 

 But with nearly all the substances enumerated, it is entirely 

 unequivocal, and with some of them quite intense. 



(2.) It is interesting to observe how, from a single drop of 

 the clear filtered liquid, we obtain distinctive evidence of the 

 presence of alkalies, or lime, or magnesia. The latter are in- 

 dicated by the milkiness of the drop, when reduced by eva- 

 poration on the platinum slip, as well as by the volume and 

 whiteness of the tache. But farther and more minute infor- 

 mation is obtained by testing the tache before ignition, and 

 again at successive stages of ignition. The volatility of the 

 three fixed alkalies and their carbonates, we have found to be 

 much greater than seems to be generally imagined. By care- 

 fully comparing them in this respect with one another, and 

 with lime and magnesia, we have been enabled to make very 

 advantageous use of the blow-pipe, in connection with test- 

 paper, in examining the tache, so as to recognise the alkalies 

 and alkaline earths severally present in the tache of felspai", 

 hornblende, serpentine, epidote, and other minerals. 



These and other habitudes of the tache, obtained with car- 

 bonated water, give this method unexpected value in the 

 quantitative analysis of minerals. It furnishes by far the 

 easiest and most speedy method of discerning the presence of 

 an alkali, or lime, or magnesia, in a mineral ; and we think, 

 therefore, that it promises to become a useful auxiliary to 

 the mineralogist, in connection with the ordinary blowpipe 

 reactions. 



(3.) By the second method, that of prolonged digestion, we 

 have actually made with carbonated water, and even with 

 simple water, a partial analysis of a number of complex mine- 

 rals. The specimens exposed to the CO2 water for forty- 

 eight hours, and to the simple water for one week, have, in 

 many instances, furnished a sufficient amount of material to 

 the liquid to admit of a quantitative examination. Thus, 

 from hornblende, actinolite, epidote, chlorite, serpentine, felspar, 

 mesutype, ^c, we have procured a quantity of ^iwe, magnesia, 

 oxide of iron, alumina, silica, and alkali, the dissolved ingre- 

 dients of these minerals severally amounting to from 0'4 to 

 1 per cent, of the whole mass. The lime, magnesia, and alka- 



