:2'52 tm some blowpipe-reactio^ns. 



III.— ON THE REACTIONS OF CHROMIUM AND MANGANESE 

 WITH CARBONATE OF SODA. 



When a mineral substance is suspected to contain manganese, it is 

 commonly tested by fusion witb carbonate of soda. But chromium 

 compounds form with, that reagent a green enamel much resembling 

 that formed by compounds of manganese. 



The chromate-of-soda enamel, however, is yellowish-green after 

 exposure to an oxidating flame, and the green colour never exhibits 

 any tinge of blue. 



The manganate-of-soda enamel, on the other hand, is generally 

 greenish-blue when quite cold. 



To avoid, however, any risk of error in the determination, the 

 ibead may be saturated with vitrified boracic acid until all the car- 

 bonic acid is expelled, and a clear glass is obtained. The chrome 

 glass will retain its green colour, whilst the manganese glass will 

 become amethystine or violet. In place of boracic acid, silica may 

 be used if more convenient. In this case, the reaction is assisted by 

 the addition of a very small amount of borax. 



IV.— ON THE DETECTION OF CADMIUM IN THE PRESENCE OF 

 ZINC, IN BLOWPIPE EXPERIMENTS. 



When cadmiferous zinc ores, or furnace-products derived from 

 these, are treated in powder with carb.-soda on charcoal, the charac- 

 teristic red-brown deposit of cadmium oxide is generally formed at 

 the commencement of the experiment. If the blowing be continued 

 too long, however, this deposit may be altogether obscured by a thick 

 coating of zinc oxide. When, therefore, the presence of cadmium is 

 suspected in the assay-substance, it is advisable to employ the fol- 

 lowing process for its detection. The substance, if in the metallic 

 state, must first be gently roasted on a support of porcelain or other 

 non-reducing body. Some of the resulting powder is then fused with 



alogie" (edition 1., 1770; ed. 2, by John Hyacinth de Magellan, 1788), although phosphor- 

 salt is mentioned as a reagent under tlie term of sal fusibile microcosmicum, and was indeed used 

 "by Cronstedt before 1758, the year in which his "Mineralogie" was anonymously published. 

 Bergmann, who followed as a blowpipe worker, states that " siliceous earth " is very slowly 

 •attacked by microcosmic salt, but he does not seem to have remarked the skeleton formation 

 in the case of any silicate. The reaction appears to have been first definitely pointed out by 

 Berzelius in his standard work on the blowpipe, published in 1821. It was therefore most 

 probably discovered by him, or perhaps — as he lays no claim to its discovery, whilst claiming 

 ■to be the originator of other tests — it may have been communicated to him by Gahn? 



