Page:Proceedings of the Royal Society of London Vol 1.djvu/291

Rh Much, however, in Mr. Pepys's estimation. remained to be done in the mechanical part of the apparatus, and in the course of various experiments on these subjects, that it might be rendered more com- modious in its application, and capable of giving correct results with the utmost minuteness.

The instmunents which he proposes consist of two tubes, one larger and one smaller, with a bottle of elastic gum to each, and a glass cylinder, or cistern, of the same length as the tubes. The larger of the tubes, containing one cubic inch, is the principal measure, and is divided into hundredths; the smaller is intended to measure fractional parts; and in this each of the former divisions is divided into ten parts, or thousandths of the cubic inch.

One of the bottles of elastic gum has attached to it a tube, which serves as a perforated stopper to the larger measure, through which any liquid to be applied to the gas under examination may be forcibly injected. When the full contraction has taken place, the measure is immersed in the cistern, ﬁlled with mercury or with water, according to circumstances, and the contraction noted. But if the surface is found not to correspond with a division of the principal measure, the smaller tube, which slides through a cork in the bottom of the cistern/is‘to be passed up till its extremity (which is open) reaches the gas contained, and the fractional part is then withdrawn by means of its elastic bottle, and measured with the greatest precision.

Mr. Pepys next proceeds to an account of various gases.in which he tried the purity by means of this apparatus, as nitrous gas, containingj—H—n- of impurity, oxygen gas “I”; atmospheric air, of which 125%; were absorbed; carbonic gas, which left Tamand sulphuretted hydrogen “,5” of impurity.

In the analysis of compound gases also, he imagines it will be found peculiarly useful. He recommends using the solutions hot, which facilitates chemical union, but prevents the absorption of carbonic and other gases by the mere water of solution, which might other- wise take place.

In order to avoid the expansion that would be occasioned by handling the measure, Mr. Pepys employs a pair of forceps, having circular extremities lined with cloth, for grasping the tube.

The elastic gum, he observes, is so little acted upon by chemical agents, that a great variety of them may be employed, and may with facility be used at any temperature.

It was on the 24th of April that Dr. Herschel ﬁrst saw the new planet Vesta; but though he saw her again on the 25th, he could not determine which of several stars he noted was the planet, for