Part 5 (1/2)

AND FIRST OF

_WATER_

Having considered all the substances that are usually found in the forenerally in a _fluid_ for with _water_, which is the principal, if not the only cause of fluidity to all the other substances that I shall place in this class

Pure water is a liquid substance, transparent, without colour, taste, or srees of heat and cold may be made to assume the three forms of a solid, of a fluid, and of air Below 32 of Fahrenheit it is ice, and above 212 it is vapour; so that in an atmosphere below 32 it never could have been known to be any thing else than a peculiar kind of stone, and above 212 a peculiar species of air

In passing froreat quantity of the principle, or matter, of _heat_, which re from a state of fluid to that of vapour, it absorbs much more; and this heat is found when the processes are reversed It has been observed, that ater becolobules, holloithin, so as to be specifically lighter than air

The degree of heat at which water is converted into vapour depends upon the pressure of the ath mountain, it boils with little heat; and when coester, or in the bottom of a deep pit, it requiresof the pressure will instantly put a stop to the boiling, and in the latter case the re of the pressure will instantly convert the heated water into vapour

The ease hich water is converted into vapour by heat, has given a great power tothe natural pressure of the atmosphere, when steam is condensed under a moveable pistern, in an iron cylinder, which was the principle of the old fire-engine, or by e the elastic power of steam to produce the saine

Water was long thought to be incompressible by any external force, but Mr Canton has shewn that even the pressure of the atmosphere will condense it very sensibly

We do not know any external force equal to that by which water is expanded when it is converted into ice, or into vapour For though the particles of water approach nearer by cold, yet when it crystallizes, the particles arrange themselves in a particular manner, with interstices between them; so that, on the whole, it takes up more room than before

Water has an affinity to, and combines with, almost all natural substances, aerial, fluid, or solid; but most intimately with acids, alkalies, calcareous earth, and that calx of iron which is called _finery cinder_, froest heat will not expel it

It has been supposed by soitation, water may be converted into a kind of earth; but this does not appear to be the case It has also of late been thought, that water is resolvable into dephlogisticated and inflaed to prove this do not satisfythat appeared till very lately, water ht be considered as a simple element By means of heat, however, it seems to be resolvable into such air as that of which the atisticated, only with a greater proportion of the forravity and teenerally beenand boiling points being the liraduated

Other substances have also been compared ater, as a standard, with respect to the capacity of receiving heat, and retaining it in a latent state, as will be shee consider the subject of heat

LECTURE XII

_Of the Nitrous Acid_

Under the head of _liquids_ I shall consider _acids_ and _alkalis_, though some of them may be exhibited in the form of air, and others in a solid form These two chemical principles are formed to unite with one another, and then they constitute what is called a _neutral salt_

Both acids and alkalis are distinguishable by their taste Another test, and etables red, and alkalis turn the syrup of violets green

Acids are generally distinguished according to the three kingdoetable_, and _animal_ The mineral acids are three, the _nitrous_, the _vitriolic_, and the _marine_

The nitrous acid is formed by the union of the purest inflaisticated air But it is usually procured fro its base, expels the nitrous acid in a liquid form On this account this acid is said to be weaker than the vitriolic

If the nitrous acid be h a red-hot earthen tube, it will be decoisticated air

Like all other acids, the nitrous acid has a strong affinity to water; but it is not capable of so enerally of an orange or yellow colour; but heat will expel this colour in the form of a red vapour, which is the saiston; and therefore when it is colourless it is said to be dephlogisticated But the colourless vapour exposed to heat, or to light, will beco this coloured vapour, becoes the skin of a yellow colour, which does not disappear till the epideriston, alkalis, metallic substances, and calcareous earth

By iston it occasions that rapid accension called _detonation_, when any salt containing this acid, especially nitre, is applied to hot charcoal, or when charcoal is put to hot nitre In fact, the charcoal burns so rapidly by isticated air supplied by the nitre