PART I.

Elements of Pharmacy.

ficient degree of heat; and all liquids, with the exception ofalcohol and ether, become solid when exposed to very low tem-peratures. The particular temperatures necessary for the pro-duction of these changes, however, are exceedingly various, butibr the same bodies they are always the same. 1 In some cases,the change is sudden, or the body instantly passes from the solidto the liquid state; in other cases, it passes through severaldegrees of softness before it be perfectly liquefied : the conver-sion of ice into water is an example of the first; the melting ofglass, of wax, and other unctuous matters, are instances of thesecond. There are some bodies, nevertheless, which cannotbe melted or fused, owing to their suffering chemical decompo-sition at a lower temperature than is required for their fusion :— a piece of wood, for instance, cannot be melted by the ap-plication of any degree of heat.

Although the melting point, In most cases, is always thesame in the same bodies, yet circumstances may vary it; andthe admixture of other substances may alter it very consider-ably. Thus, the melting point of ice, or, what is the samething, the freezing point of -water, is 32°; but, by exposingwater slowly to the action of freezing mixtures, it may be cool-ed down to 22" before it freezes. The addition of salt rendersthis point still lower, as may be seen by the following table. 2

Names of salts,

Proportion by weight dissolvedin 100 parts of water.

Freezingpoint.

Sulphate of magnesia .

25-

20-

50-

41.6

12-5

41'6

33-3

4-

8'

21-

25-5

26-

28*28-6

Sulphate of iron ....------------of zinc ....

When solids pass to the liquid state they receive an addi-tional quantity of caloric, which combines with them, but doesnot sensibly elevate their temperature, and this caloric of

1 Table, showing the degree of temperature, according to Fahrenheit's ther-mometer, at which several solid bodies melt.

Lead - - 612° \ Copper - - - 4587 3 , Fahr. 27, Wedg.

Bismuth - 476 Silver - - - 4717 ------ 28

Tin - - - 442 Iron - - - - 21637 ------ 158

Spermaceti 112°Phosphorus 100Tallow - - 92

Zinc - - 700 Sulphur ... 218

Oil of anise SO

Antimony - 809 Bees-wax - - 142lYIercury —39 Lard - - - - 97

Camphor- 303Ice ------a2

3 PS& Tram. 1788,27, quoted by Dr. Thomson, — iiysl. Chemist)

C 4

11, 4Ih edit. i. 520.