nHsrafflSBHSffl

xxiv

Elements of Pharmacy.

part r.

rAII'f T

Philosophers are not completely agreed whether it is a pro-perty only of bodies, such as a vibration of their particles', ora peculiar substance,- but the latter opinion is the one moregenerally adopted.

Under this opinion caloric is regarded as a very subtile elas-tic fluid, which penetrates more or Jess all bodies, passingreadily from one to another ; and is every where diffused. Itsparticles are supposed mutually to repel each other; and bodiesinto which it enters in any sensible quantity are increased inbulk, and undergo other changes of form. It is radiated in thesame manner as light, and in this state forms apart of the solarray." The rays are refrangible, and capable of reflection. Ithas no ascertainable gravity; and neither the addition nor theabstraction of it alters sensibly the weight of bodies. 3 It existsin two different states; in a free state, in which it is merelyloosely mingled as it were, with other bodies; and, in a latentstate, or one of intimate combination.

Regarding it as matter, the sources whence it may be ob-tained, the laws which regulate its motion and distribution, andits effects, require to be noticed.

Sources of Caloric.The known sources of caloric arc the sun, combustion, percus-sion, friction, and mixture.

a. The sun is an apparent source of caloric; but, the directaction of the sun's rays upon bodies seldom produces a tempera-ture exceeding 120°. When these, however, arc concentrated bymeans of a concave mirror, or a lens; or when means are takento prevent the communicated heat from being carried off" by thesurrounding bodies, a much higher temperature can be pro-duced. This source of caloric is not resorted to for pharma-ceutical purposes.

b. Combustion is a source of caloric highly interesting on ac-count of its utility.

When a combustible is heated to a certain degree, it is con-sumed, emitting rapidly light and caloric, until the whole sub-stance has suffered a change of properties.

The true nature of this process was first explained by Lavoi-sier, who laid it down as a chemical axiom, that " in everycase of combustion, oxygen combines with the burning body."His explanation of combustion depends on two laws: Jst.That when a cumbustible body is heated to a certain tempera-ture it immediately begins to attract and combine with the oxy-gen of the atmospheric air. 2d. This oxygen being in a state

1 The idea of caloric being motion or vibration, originated with Lord Bacon.

2 Philosophical Trans. 180?. 3 lb. 1799, p. 179.