1817,] Dr. Richard Watson. 268 
Common salt, 
Sal-ammoniac, 
Carbonate of ammonia, 
Carbonate of potash, 
Sulphate of magnesia, 
Lymington Glauber’s salt, 
were entirely fluid. A temperature of 6° being too high for the 
congelation of water saturated with salt, it is obvious that this so- 
lution could not have congealed. The subject of the congelation 
of solutions of different saline solutions was afterwards taken up, 
and very satisfactorily resolved by Sir Charles Blagden in a paper 
published in the Philosophical Transactions for 1788, to which I 
refer the reader. If we compare the freezing point at which the 
saturated saline solutions tried by Sir Charles Blagden congeal, 
with the state of Dr. Watson’s solutions, we may conclude that 
their temperature was about 251°; for the freezing point of a satu- 
rated solution of nitre is 26°, and that of a saturated solution of 
sulphate of magnesia 251°, 
Ill. Account of an Experiment made with a Thermometer whose 
+ Bulb was painted black, and exposed to the direct Rays of the 
Sun. (Phil. Trans. 1773.) 
In the beginning of July, 1772, he exposed a thermometer to 
the direct rays of the sun. It rose to 108°. On blackening the 
bulb by means of China ink, the thermometer rose to 118°. This 
experiment was carried much further by De Saussure, and the late 
Professor Robison, of Edinburgh. Saussure, by surrounding the 
bulb with charred cork, and exposing it to the sun’s rays, made it 
rise to 221° at Geneva. Professor Robison, at Edinburgh, raised a 
thermometer by similar means to 237°. 
IV. Chemical Experiments and Observations on Lead Ore. (Phil. 
Trans. 1778. 
In this paper he gives the specific gravity of different varieties of 
galena. He shows that it may be sublimed in close vessels; but 
that the highest temperature to which it can be raised is insufficient 
to decompose it. But when air is admitted to galena at a white 
heat, sulphur escapes from it, and the ore is partially reduced to 
the metallic state. He shows that in galena the lead is in the 
metallic state. He attempted the analysis of galena by the action 
of diluted nitric acid. By this means he dissolved the lead, and 
obtained a quantity of sulphur which amounted in his trials to be- 
tween 4 and 4 of the weight of the ore. The real proportion of 
sulphur in galena is a of the whole. He found that Chinese 
lead, ‘when melted, would not form the colours on its surface 
which are known to distinguish pure lead. He made a great many 
experiments to discover the cause of this difference, and at last 
ascertained that when a little tin is added to melted lead, it deprives 
it of the power of exhibiting colours on its surface. I found some 
