CHEMISTRY. 



49 



Elements incombustibles : For the metallic oxides have been 

 already described in the First Book, while treating of 



l"" 5 ^; the metals. All that is known of the oxides of phos- 

 phorus and sulphur has also been stated. We have 

 only to examine in this place, therefore, the oxides of 

 hydrogen, carbon, and azote. 



SECT. I. Of the Oxide of Hydrogen, or Water. 



Oxid of This well known liquid is found in abundance in 

 kydrogen. eve T P art ^ tne wor 'd. When pure, in which state 

 it may be obtained by distillation, it is destitute of 

 colour, taste, and smell. 



At the temperature of 40, a cubic foot of pure wa- 

 ter weighs -l.37102.19iG grains troy, or 999.0914161 

 ounces avoirdupois. Hence a cubic inch of water at 

 4O weighs 252.953 grains, and at 60 252.72 grains. 

 The specific gravity of water is always supposed 

 1.000, and it is made the measure of the specific gra- 

 vity of every other body. 



When cooled down to 32, it crystallizes and be- 

 comes ice. At 212 it boils, and is converted into 

 steam, an elastic fluid, invisible like air, and about 

 J800 times more bulky than water. The boiling 

 point of water is somewhat altered by dissolving salt 

 in it. Some salts raise the boiling point, others lower 

 it a little, while some produce both effects according 

 to the proportion employed. 



Water is not altered by heat. It absorbs a little 

 air, and a certain proportion of all gases exposed to 

 it. By long boiling, or by being placed in an ex- 

 hausted receiver, it is freed from the greatest part of 

 this air. 



Water has no action on the simple combustibles 

 while cold ; but, at a red heat, charcoal decomposes 

 it. The action of phosphorus is not known. Sul- 

 phur, as far as is known, does not decompose it. 



Of the metals, iron, zinc, antimony, and tin, de- 

 compose it when assisted by heat ; silver, gold, cop- 

 per, and platinum, have no effect on it. The action 

 of the other metals has not been ascertained. The 

 metallic bases of the alkalies and earths decompose it 

 with great rapidity, at the usual temperature of the 

 atmosphere. 



Water dissolves the alkalies and alkaline earths. 

 The earths proper are insoluble in it. It dissolves 

 also acids and salts, and is capable of combining with 

 a great variety of bodies. Water unites to bodies 

 two different ways. Some it dissolves, and the com- 

 pound becomes liquid like water. In this way it 

 dissolves sugar, common salt, and many other bodies. 

 Other bodies combine with it without losing their 

 solidity. The water loses its liquid form, and as- 

 sumes that of the body with which it unites. In this 

 way it combines with lime, with alumina, with many 

 salts, and with various metallic oxides. When the 

 compound of water with another substance remains 

 liquid, the proportion of water is unlimited ; but 

 when the compound formed is solid, the water com- 

 bines always in a certain determinate proportion. To 

 the first kind of compound, the name of solution has 

 been given ; to the second, the term hydrate has been 

 applied. Thus, slacked lime is called hydrate of 

 lime; the crystals of barytes and strontian are called 

 hydrates of Larytcs and strontian. Most of the me- 



VL. VI. PART I. 



tallic hydrates have lively colours, a strong taste, and Elemenu 

 are easily soluble in acids ; while the oxide which con- c 

 stitutes the base of the hydrate is usually duller in - ^ em "^j/ 

 its colour, often tasteless, arid always more difficultly 

 soluble in acids. Tlie hydrate of copper is blue, 

 that of nickel and iron green, that of cobalt red, and 

 that of tin white. 



All the gases, in their usual state, contain a quan- 

 tity of water, from which they are best freed by ex- 

 posure to a very low temperature. 



The ancients considered water as an elementary 

 substance. Van Helmont endeavoured to prove, that 

 plants could be nourished by pure water alone, and, 

 of course, that it could be converted into all the sub- 

 stances found in vegetables. Boyle thought that, by 

 long digestion in glass vessels, it could be converted 

 into silica. His experiment was confirmed by Mar- 

 graff. But Scheele and Lavoisier proved, that the 

 silica was obtained by the decomposition of the glass 

 vessel in which the experiment was made. Mr Ca- 

 vendish, in 1781, ascertained that water is a com- 

 pound of oxygen and hydrogen, nearly in the pro- 

 portion of seven parts of the former, and one of the 

 latter ; and this discovery was confirmed by a num- 

 ber of very laborious and rigid experiments. 



SECT. II. Of Carbonic Oxide, 



The substance at present known by the name of Carbonic 

 carbonic oxide, is a gas which was confounded with ox >de. 

 carbureted hydrogen, till Dr Priestley drew the at- 

 tention of chemists to it, in a dissertation which he 

 published in defence of the doctrine of phlogiston. 

 It was examined, in consequence, by Mr Cruik- 

 shanks, who showed it to be a compound of oxygen 

 and carben, and not of hydrogen and carbon, as 

 Priestley had supposed. Clement and Desormes also 

 analysed it with the same result. 



It may be obtained most readily by mixing toge- How ob- 

 ther equal weights of iron filings and chalk, each as 

 dry as possible, and exposing them to a red heat in 

 an iron retort. A gas comes over in abundance. It 

 consists partly of carbonic acid, partly of carbonic 

 oxide. The first gas is removed by washing in lime- 

 water. The carbonic oxide remains behind. 



Carbonic oxide is invisible, and possesses the me- luproptr- 

 chanical properties of common air. Its specific gra- tle *- 

 vity is 0.95G, that of air being 1.000. No animal 

 can breathe it without death. No combustible sub- 

 stance will burn in it. 



It burns with a blue flame, giving out but little 



light, and is wholly converted into carbonic acid ga*. 



When mixed with oxygen ga^, and kindled by means 



of an elfctric spark, 100 parts of it require 45 parts 



by bulk of oxygen gas for complete combuction. 



The result is about 90 parts of carbonic acid gas. 



From this experiment it has been deduced, that car- 



bonic oxide il composed of tioo. 



41 carbon. 



59 oxygen. 



100 



The simple combustibles have but little action on 

 this gas. Hydrogen has none, even at a red 'teat, 

 nor charcoal, nor sulphur. But it dissolves a little 



