440 
POPULAR SCIENCE REVIEW. 
METALLUKGY, MINERALOGY, AND MINING. 
TAe Specific Gravity of JRubies and Diamonds. — Mr. Greville Williams, 
F.R.S., says that in his paper entitled Researches on Emeralds and 
Beryls,’’* * * § he stated that the artificial rubies made by him by Gaudin’s 
process had a lower specific gravity than that of the true ruby. He there 
assumed the density of the ruby to be 3*5.3, on the authority of Brisson,t 
and that of the sapphire as 3*56, according to Muschenbroek.J Having 
occasion, in extending his experiments on the subject, to take the specific 
gravity of several rubies and sapphires, he found their density to be very 
much higher than the numbers given in Gmelin’s ‘‘ Chemistry.” On re- 
ferring to other works, § he found the numbers given in them to be generally 
between 3*9 and 4*0 ; Prof. Church also found a blue sapphire to have a 
density of 3*979, and a yellow one 4 030. His own determinations, made 
upon very fine stones, gave him for rubies 8*95, and for sapphires 3*98. 
Assuming 3*95 as the average specific gravity of the ruby, it will be seen 
that Gaudin’s rubies, as first made by him (Williams), were 0*5 lower in 
density than the native ruby, instead of 0*08 as given in his former com- 
munication. He has, however, recently succeeded in preparing some fresh 
specimens of artificial rubies by the same process, but with a higher density, 
namely 3*7 ; this number is only 0*25 lower than the native ruby, and he 
thinks it probable that the true density of the ruby might be attained if the 
frothing, which takes place to a greater or less degree under the intense 
heat of the oxyhydrogen blowpipe, could be completely avoided. — Vide 
Chemical News,” August 29. 
Hungarian Transylvanian Dacites . — These would appear, from the recent 
researches of Herr Dr. C. Doelter (“ Verhandl. der Geol. Reich sanstalt,” 
1873, No. 6, 107), to be mostly hornblende and augite andesites, the former 
always having quartz as an essential constituent, the latter appearing to be 
mostly free from this mineral. The essential constituents of the dacites are 
a plagioclase felspar, quartz, sanidine, hornblende, biotite, augite, magnetite, 
and apatite, the accessory minerals being chlorite and epidote. The quartz 
occurs as crystals in dihexagonal pyramids, and in grains for the most 
part porphyritically distributed. Sanidine is a constant constituent in all 
varieties of the dacites, varying in amount from ten to twenty-five per cent, 
of the whole of the felspars, and is usually distributed in a fine state of 
division through the ground-mass. The structure of the quartz-bearing 
andesite (hornblende andesite) admits of its being divided into three groups 
— granitoporphyritic, porphyritic, and trachytic, the latter much resembling 
the true trachyte. The sanidine in these varieties never exceeds in amount 
fifteen per cent, of the felspar ; the hornblende crystals are very distinct and 
terminated at both ends, and augite is often present. 
Soldering Iron and Steel , — It appears from a paper published by Herr 
Rast in the “Bayerisches Industrie- und Gewerbe-Blatt,” that so-called 
German silver may be applied to soldering steel to iron and iron to copper. 
* Proceedings of the Royal Society,” 1873, No. 145, p. 409. 
t Gmelin’s “ Chemistry,” Cavendish Society’s translation, vol. iii. p. 305. 
X Loc. cit. 
§ “ Brooke and Miller,’* Watts’s Chem. Diet.,” Rammelsberg,” &c. 
