405 
of Edinburgh, Session 1868 - 69 . 
in the Sulphurating of Metals,” proves that when sulphur and iron 
are heated together, and combine to form the sulphide of iron, the 
process is one not of inflammation, as might appear on a hasty sur- 
vey of the phenomenon, but of incandescence, which lasts only 
during the short time combination goes on, and without any of the 
essentials of combustion. He annexes some inferences in respect 
to the connection between heat and light, which I may have to 
revert to under a future head, as in some measure anticipating a 
great modern doctrine. The experiment, a striking one, has been 
rendered long familiar in consequence of Dr Hope, who assisted 
Hutton in this inquiry, having constantly made it the subject 
of brilliant demonstration in his lectures, as many of us must 
well remember. 
In 1800 Sir George Mackenzie presented to the Society a 
very conclusive inquiry as to the combustion of the diamond. 
It had been burnt, and its nature deduced from the product, in 
various complex ways, by several eminent chemical philosophers. 
But Sir George had the merit- of showing how it might be con- 
sumed in a simple muffle with unaided heat at 15° of Wedge- 
wood’s pyrometer, — that steel might be made by heating iron in 
contact with its dust, — and that, by duly heating a mixture of pul- 
verised iron with a fourth of its weight of diamond dust, a fused mass 
may be obtained which is quite undistinguishable from cast-iron. 
I conclude these chemical notices with a second original in- 
vestigation of great excellence and interest by Dr Hope. It has 
been long well known that, as water cools down from a mean 
temperature, it contracts, and consequently the cooled particles 
sink until the thermometer indicates about 39 0, 5 Fahr. ; that on 
farther cooling, however, this general law which regulates the 
cooling of liquids is upset ; that the water then actually expands, 
and consequently the cooled particles now rise ; and that this ex- 
pansion continues, till at 32° a much greater expansion suddenly 
takes place, when the water is converted into ice. The contrary 
phenomena, of course, occur as water heats from 32°. It con- 
tracts till the temperature rises to 39°‘5, and after that expands 
according to the general law. But the fact of the density of water 
thus deviating from the general law which governs the influ- 
ence of heat on liquids, had been often called in question by high 
