243 
Diamond used in Jacquelain’s experiments, 
3-33 
Jacquelain. 1 
Specific gravity, as given by Henry, 
355 
Henry ? 
Well-crystallized Brazilian diamond, weigh- 
ing 0*5761 gramme in the Edinburgh > 
3-48 
Playfair. 3 
Museum, ... J 
Mean sp. gr., 
3-461 
If we reject the second Borneo diamond of Rivot, which has too 
low a specific gravity, we have a mean sp. gr. of 3"48, which is the 
same number as that found by Wilson Lowry for the mean specific 
gravity of u his beautiful collection of crystallized diamonds'’ 
(Thomson’s Mineralogy, vol. i. p. 46). 
It is to be expected that the experimental determination of the 
specific gravity of diamonds should be rather above than below the 
truth ; for we are aware that they all leave a minute quantity of 
ash on burning, and that this ash, according to Petzhold, contains 
silica and iron. 
2. Graphite. 
This variety of carbon is often impure, being not unfrequently 
contaminated with upwards of five per cent, of earthy impurities. 
Recorded specific gravities upon such impure specimens are of no 
value for the mean result as regards pure graphite. The following 
determinations are all those which I can find upon specimens which 
have been chemically examined to establish their purity : — 
Natural graphite, . . 2*27 
Do. . . 2*25 ^ 
Do. . . 2-32 J 
Graphite of iron furnaces, . 2-33 
Natural graphite, in fine crystalline plates, 2* 14 1 
Do. do., another variety, 2*22 j 
Do. do., do., 2-23 
Regnault. 4 
Schrader. 5 
Karsten. 6 
Breikhaupt. 6 
Kengott. 7 
1 Jacquelain, Ann. de Ch. et Thys, [2], vol. xx. p. 459. 
2 Henry’s Mineralogy, vol. iv. p. 19. 
3 Experiment made for this paper. 
4 Regnault, Ann. de Ch. et Thys., vol. lvi. p. 37. 
5 Schrader, Annals of Philosophy, vol. i. p. 299. 
6 As quoted in Bottger’s Specifiche Gewicht. 
7 Kengott, Wien Akad. vol. xiii. p. 469. 
