58 M. Pfaundler on the Influence of the Physical 



we can pronounce any opinion as to the importance or unim- 

 portance of these investigations. 



The method adopted was the method of mixtures ; and an 

 apparatus was used which had been originally devised by Re- 

 gnault, and which Pfaundler recommends for its convenience and 

 accuracy. It consists essentially of a tin-plate canister shaped 

 like a bottle and supported on uprights by means of two lateral 

 axes, so that it can be tilted up ; in the neck of the canister a 

 stout large-sized test-tube, or eprouvette, is fixed by means of 

 a tightly fitting cork. The canister contains water, which is 

 kept boiling by means of a spirit-lamp, while the steam emerges 

 through a lateral tube which at the same time serves as one of 

 the axes. The substance under investigation, dried at a constant 

 temperature, was placed in the eprouvette, and the whole weighed ; 

 the mouth of the eprouvette was closed by cotton-wool, and the 

 substance could thus be heated to the temperature of boiling 

 water ; control experiments indicated what length of time was 

 necessary for this purpose. No thermometer was used; the 

 temperature was obtained from the reduced barometric height 

 by means of boiling-point tables. 



When a given weight of the substance had been raised to the 

 proper temperature, the apparatus was tilted so that the sub- 

 stance fell into the water of a calorimeter. It is needless to 

 enter upon the mode in which this was effected, or the precau- 

 tions taken to avoid sources of error. There was nothing essen- 

 tially new in the construction of the calorimeter; suffice to say 

 that great care was taken to have very delicate and accurate 

 thermometers, by means of which T ^ of a degree could be 

 read off, and that the calorimeter was provided with a stirrer, 

 which could be moved with regularity by means of wheelwork. 

 Those who are familiar with the construction of Regnault's ap- 

 paratus for specific heat will remember that the heating-apparatus 

 is fixed and the calorimeter moveable, while in the present appa- 

 ratus the exact opposite is the case — an arrangement which 

 Pfaundler considers to have several advantages. The eprouvette 

 was weighed after the experiment ; and the difference between 

 the two weighings gave the weight of the substance taken. 



Several kinds of earths present peculiar difficulties. Light 

 dusty soils remain for a long time floating on the surface of the 

 water before they are melted and sink down. Substances rich in 

 humus and turf do not sink at all, and therefore require special 

 arrangements : they are pressed in small cylinders of tinfoil the 

 size of a lead pencil, from six to nine of which can be brought 

 into the eprouvette, the water value of the tinfoil being of course 

 taken into account. With very light soils this was inapplicable, 

 and they were stamped into small brass boxes of the thinnest 



