When liquids are mixed together, they either unite in all proportions, or in certain determinate proportions only; or they cannot be united, but separate, howsoever carefully they be mixed together; or they decompose one another.

I. Table Of Pharmaceutical Liquids Which Unite When Mixed Together In All Proportions, And Do Not Afterwards Spontaneously Separate

Water with alcohol.

---------------nitric acid.

---------------sulphuric acid.

Alcohol with ether.

----------------with some volatile oils.

Sulphuric acid with nitric acid. Fixed oils with petroleum.

---------------------volatile oils.

---------------------fixed oils.

Volatile oils with petroleum. ---------------------, volatile oils.

When these liquids are mixed together, such a mutual penetration takes place, that every portion of the mixture contains the same proportions of both ingredients; and this is the case, although there may be the greatest difference in the specific gravity of the individual liquids. Agitation assists the rapidity of this effect very much, but the mixture is never perfect until some time afterwards. If, on the contrary, agitation be not employed, the mixture is always more quickly effected when the denser liquid is added to the rarer; for in the opposite case a long period often elapses before it is completed. A partial muddiness occurs when even transparent liquids of different densities are mixed together, and continues until the mixture be perfect; but when it is completed, the compound is homogeneous, and the liquids do not afterwards separate from one another.

As the density and specific gravity of a compound thus formed are always greater than the mean, caloric is evolved during the mixture. In some cases the quantity is scarcely sensible; but in other instances it is capable of affecting considerably the thermometer. If fixed and volatile oils be mixed, the temperature is not very sensibly raised; but if alcohol and water are mixed, the evolution of heat is very sensible; and if four parts of sulphuric acid and one part of water, both at 32°, be mixed together, the temperature rises to 212°. When equal parts of sulphuric acid and water are mixed, the density is augmented by 13 per cent.; of nitric acid and water, the increase is equal to 1/12; and when water and pure alcohol are mixed, it is rather more than 1/28 of the whole weight. These mixtures are cases of real chymical combination; the force which holds them combined being that of chymical attraction exerted between the integrant particles of the two liquids.

II. Table Exhibiting A List Of The Pharmaceutical Liquids Which Unite With Each Other Only In Certain Proportions

Water with ether.

--------------volatile oils.

Alcohol with some volatile oils.

-----------------petroleum.

Ether with volatile oils.

--------------petroleum.

Volatile oils with petroleum.

Water dissolves rather less than one tenth of its bulk of sulphuric ether; and the proportion of volatile oil it takes up is also very minute, being scarcely more than is sufficient to communicate the odour of the oil to the water, without any other of its properties. Although alcohol unites readily with the volatile oils, yet the quantity of each is limited; and the proportion of petroleum which alcohol dissolves is very small. The proportions of volatile oils and petroleum which ether dissolves are considerable.

The affinity of the compounds of this table is much weaker than that of the former; which, "with the difference between the cohesion of the particles of the two liquids, limits the combination to certain proportions." They are also more easily decomposed; for, if a spirituous solution of volatile oil be poured into water, the alcohol leaves the volatile oil to unite with the water, while the greater part of the separated oil swims on the surface of the new compound.

III. Table Exhibiting The Principal Pharmaceutical Liquids Which Do Not Sensibly Combine In Any Proportion

Water with petroleum.

--------------fixed oils.

Fixed oils with alcohol.

--------------------ether.

Mercury with water.

--------------------alcohol.

--------------------ether.

--------------------volatile oils.

---------petroleum.

•58 Elements of Pharmacy. part i.

In these cases, the affinity between the two liquids is not sufficient to overcome the cohesion between the particles of each liquid. The spreading of oil, however, upon the surface of water, and adhering to it, is supposed to depend on the exertion of some degree of affinity, although less than is requisite to produce a combination of the two liquids.

If a liquid have an affinity for one of the constituents of another liquid, although not for the liquid itself, it frequently decomposes it, and forms new compounds.

IV. Table Of The Principal Pharmaceutical Liquids Which Decompose Each Other

Nitric acid by all liquids, except water and sulphuric acid. Sulphuric acid by all liquids, except nitric acid and water. The combinations of solids reduced to the liquid state are regulated by the very same laws as those of proper liquids.