48 
DR. T. ANDREWS ON THE PROPERTIES OF MATTER IN THE 
have examined with care the behaviour of a mixture of nitrogen and carbonic acid 
gases under varied conditions of pressure and temperature. According to the defini¬ 
tion I ventured formerly to give of a vapour, viz., that it is a gas at any temperature 
below its critical point, that is to say, at any temperature at which it can be 
changed by the application of external pressure to the liquid state, carbonic acid is a 
vapour at temperatures below 31° C., and a gas proper at higher temperatures. 
Accordingly the properties of the mixture of nitrogen and carbonic acid have been 
examined at temperatures both above and below the critical point of pure carbonic 
acid. 
The gaseous mixture, carefully dried, after flowing through the tube in which it was 
to be compressed, was collected over mercury and analysed. After all reductions were 
made its composition was found to be 
3 vol. COo and 4'05 vol. N. 
At the conclusion of the long series of experiments now to be described, which 
occupied several months, during which this mixture was exposed from day to clay to 
filled with its packing, was strongly clamped upon the edge of a table, the flat surface resting on 
the table, and the steel screw afterwards turned till it passed through the packing and entered the 
table for a short way. On removing the flange from the table, the leather was always found to project 
beyond the surface of the brass; it was cut away till it formed a thin cylinder round the screw, which 
cylinder was afterwards strengthened by tying it with a silk thread. I have been thus minute in 
describing this operation, as a screw successfully packed in this way will resist for many months a 
pressure of several hundred atmospheres. The upper flange which carried the glass tube was traversed 
by a cylindrical cavity terminating in a hollow cone, and the glass was fashioned into a form which, 
when covered with its packing, fitted into this cavity. The packing was effected by rolling round the 
glass cone and cylinder several strands of a fine hempen thread covered with shoemaker’s wax, which 
was applied slightly heated. The flange was then warmed, and the glass tube very firmly pressed down 
into its place, and the whole allowed to cool. A junction of this kind will also bear a pressure of 
several hundred atmospheres without yielding.” 
The following is given in the text of the same draft:— 
“ So perfectly did the apparatus work that in a long investigation, extending over several months, 
during which the apparatus was never dismounted, I was able without any difficulty to make a con¬ 
tinuous series of experiments at pressures varying from 50 to 300 atmospheres, and to read the changes 
of volume of the gases of these pressures in glass tubes with almost as great ease as an ordinary 
barometer. One precaution only requires to be mentioned. If the pressure is either largely augmented 
or diminished in the course of an experiment, the readings should not be made for some time after, as 
the apparatus, without the slightest leakage, takes time to adjust itself to the new condition. I presume 
it is the slow change of volume in the leather packings to which this is due. Indeed, the effect is equally 
marked on taking off the pressure suddenly as on augmenting it. The mercury in the manometer will 
rise, in the former case, visibly to the eye for some time. When working at very high pressures, I was 
formerly in the habit of making the observations as quickly as possible after each augmentation of 
pressure, but since I discovered the true action of the apparatus I have always given time for all the 
parts to adjust themselves to the new condition, when the readings can be made with great ease and 
accuracy.” 
