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there remained a certain quantity, about to of the entire volume, or about 3.5 to 5 per cent.

This permanent gas cannot be nitric oxide nor oxygen; for the current of nitrous oxide being made to pass successively through strong solutions of sulphate of iron and of pyrogallate of potassium, these solutions did not change colour.

The only known permanent gas that could be disengaged is nitrogen. It is a known fact that nitrate of ammonium, in presence of spongy platinum, is decomposed at 160° into nitrogen, nitric acid, and water; the same decomposition of a part of the salt could have been effected by the asperities of the inner surface of the retort. This quantity of nitrogen would exert a considerable influence on the specific gravity of the gas. The theoretical specific gravity of pure nitrous oxide is 1.524; but being mixed with nitrogen to an amount of 3.5 to 5 per cent., it should be found much smaller, 1.504 to 1.496 respectively. This result, however, does not accord with actual experiment. The specific gravity of nitrous oxide, prepared from nitrate of ammonium, was determined according to the method of Bunsen ('Gasom. Methoden,' von R. Bunsen); for that purpose I used a balloon of 200 cubic centims. Four experiments gave the following results:-1.531, 1·525, 1·529, and 1.527: the mean value is 1.528, agreeing very well with the theoretical specific gravity of pure nitrous oxide, but giving a difference of 0.024 to 0.032 from the specific gravity that would have been found if the gas had been mixed with nitrogen. These differences are too large to be accounted for by experimental errors.

An analysis of nitrous oxide was made according to a somewhat modified method of Frankland and Ward. The hydrogen used in these experiments was obtained from the electrolytic decomposition of water, and the oxygen was generated by heating mercuric oxide. To ensure that the mercuric oxide is free from nitrogen, it must be prepared by precipitating corrosive sublimate with caustic potash.

Three analyses of air gave the following satisfactory results :

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The following are the results of the analysis of nitrous oxide:

I. Nitrous oxide obtained from the liquid nitrous oxile of an iron bottle.

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Hence the volume of the hydrogen 146-23, the volume of the oxygen 57-76, and the contraction after the second explosion 46-69.

The remaining volume (160·19) is a mixture of only nitrogen and oxygen, where the amount of oxygen is 57.76-1× 46-69-42-20; hence the volume of the remaining nitrogen 160·19-42-20-117.99. This volume is by 0.6 larger than the volume of the nitrous oxide used; hence the amount per cent. is 0.52.

The amount of hydrogen that remained after the first explosion is ×

46.69 31.12; therefore the amount of hydrogen required to combine with the oxygen of the nitrous oxide is 146-23-31.12-115-11; hence the volume of the oxygen contained in the nitrous oxide is equal to =57-55, differing by 1.96 per cent. from the calculated volume of oxygen, which is 117.39 =58.69.

2

Hence in 100 volumes of nitrous oxide we find :

115.11
2

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II. Nitrous oxide obtained by heating nitrate of ammonium.

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The only analysis of nitrous oxide I found in Bunsen's Gasom. Methoden' is on page 56. Here Quincke gives the results of an analysis of nitric oxide, to which is added a measured quantity of nitrous oxide in order to effect the explosion.

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Hence we find, on the supposition that the nitrous oxide is pure, the amount of nitrogen and oxygen in the nitric oxide in 100 volumes :-

Nitrogen...
Oxygen

By experiment. Calculated.

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But, on the supposition that the nitric oxide is pure, this analysis gives results according with my own.

In 100 volumes of nitrous oxide we find

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The general result of these analyses is :----

(1) The volume of the oxygen in the nitrous oxide is smaller than the volume of the nitrous oxide used by 0-61 to 2.13 per cent.

(2) The volume of the nitrogen is larger than the volume of the nitrous oxide used by 0.38 to 1.66 per cent.

That the volume of the oxygen is smaller than half the volume of the nitrous oxide used can be explained by the presence of a certain quantity of nitrogen, ranging from 0.61 to 2.13 per cent., a quantity much smaller than the total amount of nitrogen mixed with the nitrous oxide, which was found to be between 3.5 and 5 per cent.

That the volume of the nitrogen contained in the nitrous oxide is larger than the volume of the nitrous oxide used could be explained by the presence of a gas containing more nitrogen in a molecule than nitrous oxide, for instance N, O; such a gas, however, is not known.

It will be observed that these analyses do not agree among themselves very nearly; and having been prevented from making more experiments, I will not venture to draw any conclusions from these results, as more analyses should be made, chiefly because the apparatus with which they were performed was somewhat defective with regard to the diameter of the glass tubing connecting the absorbing with the measuring tube.

Faraday was the first who observed an anomaly with nitrous oxide; his results were very uncertain as to the pressure of its saturated vapour. At a temperature of 0° F. this pressure amounted to 19-05 atmospheres when working from lower to higher temperatures; but after waiting a day he found 24.40 atmospheres, consequently a difference of 5·35 atmospheres. This discrepancy he ascribed to the gas being a mixture of two different bodies soluble in each other but differing in the elasticity of their vapour.

Stefan (Sitzungsber. der K. Akademie der Wissenschaften zu Wien, Bd. lxxii. 1875), in his researches on heat-conduction of gases, also found the nitrous oxide mixed with another gas. He says, "Von diesem Gase wurde vor dem Abschlusse der Durchleitung durch den Apparat eine Probe in einer Absorptionsröhr über Wasser aufgefangen. Nach zwei Tagen war das Gas bis auf einen etwas über 10 Procent des ursprünglichen Volumens betragenden Rückstand (Stickstoff) verschwunden."

Eighth Report of the Committee on the Treatment and Utilization of Sewage, reappointed at Bristol, 1875, and consisting of RICHARD B. GRANTHAM (Chairman), C.E., F.G.S., Professor A. W. WILLIAMSON, F.R.S., Dr. GILBERT, F.R.S., Professor CORFIELD, M.A., M.D., WILLIAM HOPE, V.C., F. J. BRAMWELL, C.E., F.R.S., and J. WOLFE BARRY, C.E.

YOUR Committee have during the past year, ending 24th March, 1876, been able to conduct more complete observations at Breton's Farm, near Romford, and have been also able to test experimentally the value of last year's observations by having analyses made of samples of sewage and effluent water kept under various conditions. The expense attending this year's experiments has been generously borne by a Member of the Association.

From Table I. it appears that the quantity of sewage received from the town was greater than in any year during the period over which the Committee's observations extend, not excepting the year 1872-73, when the rainfall was larger by 3 inches than this year; it is therefore clear that the quantity of sewage proper received from the town has increased steadily year by year, thus:

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It should be observed again that, as stated in last year's Report, it has not been possible during the past two years to gauge the sewage directly in the distributing-trough, and so the amount is calculated as follows:-the "day" sewage from gaugings taken in the sewers during the working hours of the engine, and the "night" sewage from the difference in the contents of the tanks at the times of stopping and starting the engines night and morning. It is worthy of note that while the weekly average of the noonday atmospheric temperatures varied from 31° to 79° Fahr., the average temperatures of the sewage only varied from 55° to 70° Fahr.

Table II. is given again after a lapse of two years, during which it was impossible for want of funds to have a sufficient number of analyses made.

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