Progress of Invention. 38i 



PROGRESS OF INVENTION. 



Aventurine. — This beautiful substance, which has long been an 

 object of imitation, is a species of quartz, that contains throughout 

 its mass a number of brilliant spangles of mica. The Venetians 

 very early succeeded in producing a compound which rivalled that 

 formed by nature ; and as they preserved the secret of its manu- 

 facture, it continued to form a lucrative article of commerce. A 

 mode of making a kind still more exquisite than the Venetian has 

 been recently discovered by M. Pelouze. The spangles in the Aven- 

 turine manufactured in the glass works of Venice consist of metallic 

 copper, the mass being tinged throughout a delicate brown, by oxide 

 of iron ; and an excellent imitation was obtained by MM. Fleury 

 and Clemandot, by keeping fused, at a high temperature, for twelve 

 hours a mixture containing three hundred parts pounded glass, forty 

 parts protoxide of copper, and eighty parts oxide of iron, and then 

 allowing the mass to cool very gradually. The Aventurine of M. 

 Pelouze is of a light green tint, which is much more pleasing than 

 brown, and is produced by bichromate of potash. He fuses together 

 two hundred and fifty parts fine sand, one hundred parts carbonate 

 of soda, fifty parts carbonate of lime, and forty parts bichromate of 

 potash. The latter is decomposed by the heat into oxide of chromium, 

 and neutral chromate of potash ; and the neutral chromate is decom- 

 posed by the silex, silicate of potash and oxide of chromium being 

 formed, and oxygen liberated. If an excess of bichromate is employed, 

 the transparency of the product is impaired, and brilliant spangles 

 of sesquioxide of chromium are diffused through it. When the proper 

 proportions are used, the artificial gem obtained yields only to the 

 diamond in lustre ; it is hard enough to cut glass, and yet it is 

 worked with great facility. To distinguish it from that obtained at 

 Venice, it has been properly termed " Chrome- aventurine." 



The Nature op Ammonia. — It has been for some time a question 

 whether or not ammonia is the oxide of a metal presumed to consist 

 of H 4 N. The strongest argument in favour of its metallic nature has 

 been founded on the fact that an amalgam of mercury may be ob- 

 tained by means of ammonia. The argument derived from this has, 

 however, been rendered extremely doubtful by the researches of Dr. 

 C. M. Wetherill. The so-called ammonia amalgam possesses phy- 

 sical properties exactly similar to those of the other amalgams ; but 

 they are found accompanied by one of a suspicious character — the 

 mass gradually shrinks of itself, and becomes resolved into ammonia 

 and mercury. It appears certain, from the experiments of Dr. 

 Wetherill, that the so-called amalgam is merely a mixture of ammo- 

 nia, sodium amalgam, and mercury, swollen up by the bubbles of 

 hydrogen set free during the process used in forming it, and retained 

 by some of the sodium amalgam used as a medium from the pro- 

 duction of the amalgam of ammonia. The sodium is thus kept out 

 of contact with the solution of ammonia salt ; but it becomes gra- 

 dually oxidized, and the swelling subsides. That such is the nature 

 of the product obtained appears certain ; since the hydrogen to 



