A text-book on chemistry : for the use of schools and colleges . his gas. Besides these, there are foundin it variable quantities of the vapor of water, and tracesof ammonia, sulphureted hydrogen, and carbureted hy-drogen. It is a colorless, invisible, elastic substance, 815times lighter than water, and is taken as the standard ofcomparison for the specific gravity of gases. Its specificgravity is, therefore, = l-000. One hundred cubic inch-es of it weigh, at the mean temperature, and pressure verynearly 31 grains. There are many methods by which the analysis of theair can be effected. Ures eu
A text-book on chemistry : for the use of schools and colleges . his gas. Besides these, there are foundin it variable quantities of the vapor of water, and tracesof ammonia, sulphureted hydrogen, and carbureted hy-drogen. It is a colorless, invisible, elastic substance, 815times lighter than water, and is taken as the standard ofcomparison for the specific gravity of gases. Its specificgravity is, therefore, = l-000. One hundred cubic inch-es of it weigh, at the mean temperature, and pressure verynearly 31 grains. There are many methods by which the analysis of theair can be effected. Ures eudiom-eter, Fig. Ill, which consists of asiphon tube, closed at one end andopen at the other, may be used forthis purpose. Into the closed branchof the instrument, which is also grad-uated, a measured quantity of air isintroduced, and to it is added anequal volume of hydrogen. Thebend of the tube is occupied by wa-ter, as shown in the figure, a columnof air intervening between this water and the open ex-tremity of the tube. On this the thumb is closely pressed,. ^J Of what is the atmospheric air composed? What is its specific grav-ity? What is the weight of 100 cubic inches of it ? How may it be an-alyzedby Ures eudiometer? ANALYSIS OF THE AIR. 191 as represented, and an electric spark passed through theinstrument by the aid of its platina wires. This sets thegases on fire ; the column of air beneath the thumb actinglike a spring to repress the movement at the time of theexplosion. The amount of gas then left is ascertained onthe divisions, and one third of the deficit represents thequantity of oxygen originally present. To enable the experimenter to operate on larger quan-tities of gas, Brunners instrument may Fi 178be used. It consists of a tube, a be, with ^_^_v^-v-^three bulbs blown upon it; these bulbs Xa^^~/^F\are filled with cotton which has been im-pregnated with melted phosphorus. Thetube is attached, by means of a cork, toa glass vessel, d, filled with mercury. Onopeni
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