DIAMONDS. 221 



At the risk of repeating an experiment shown so well at this table 

 by Professor Dewar, I will heat a diamond to a high temperature in 

 the oxyhydrogen blowpipe and then suddenly throw it in a vessel 

 of liquid oxygen. Notice the brilliant light of its combustion. I want 

 you more especially to observe the white opaque deposit forming in the 

 liquid oxygen. This- deposit is solid carbonic acid produced by the 

 combustion of the carbon. I will lead it through baryta water, and 

 you will see a white precipitate of barium carbonate. With a little 

 more care than is i)ossible in a lecture I could perform this experiment 

 quantitatively, leading the carbonic acid and oxygen, as they assume 

 the gaseous state, through baryta water, weighing the carbonate so 

 formed, and showing that 1 gram of diamond would yield 3.666 

 grams of carbonic acid — the theoretical proportion for pure carbon. 



Some crystals of diamonds have their surfaces beautifully marked 

 with equilateral triangles, interlaced, and of varying sizes. Under the 

 microscope these markings appear as shallow depressions sharply cut 

 out of the surrounding surface, and these depressions were supposed 

 by Gustav Rose to indicate the probability that the diamonds at some 

 previous time had been exposed to incipient combustion. Eose also 

 noted that striations appeared on the surface of diamonds burnt before 

 the blowpipe. This experiment I have repeated on a clear, smooth 

 diamond, and have satisfied myself that during combustion in the field 

 of a microscope, before the blowpipe, the surface becomes etched with 

 markings very different in character from those naturally inscribed on 

 crystals. ,The artificial strise are cubical and closer massed, looking as 

 if the diamond during combustion had been dissected into rectangular 

 flakes, while the markings natural to crystals appear as if produced by 

 the crystallizing force as they were being built up. 



I exhibit on a diagram a form of graphite from the Kimberley blue 

 ground (reproduced from M. Moissaii's work), which in its flaky crys- 

 talline appearance strangely resembles the surface of a diamond whose 

 internal structure has been partially dissected and bared by combustion. 

 It looks as if this piece of graphite was ready to separate out of its 

 solvent as diamond, but owing to some insufficient factor it retained its 

 graphitic form. 



PHYSICS OF THE DIAMOND. 



The specific gravity of the diamond is from 3.514 to 3.518. For com- 

 parison, 1 give in tabular form the specific gravities of the different 

 varieties of carbon : 



Amorphous carbon 1. 450 to 1. 700 



Graphite 2. 110 to 3. 000 



Hard gas coke 2. 356 



Bort 3. 470 to 3. 490 



Carbonado 3. 500 



Diamond 3.514 to 3.518 



