132 Dr. J. A. Harker on the Specific 



on a vertical shaft driven by a small electric motor. This 

 arrangement has the great advantage of leaving a relatively 

 large proportion of the space in the calorimeter free for 

 the introduction of the hot body, without undue risk to the 

 thermometer. The two calorimeters used in the experiments 

 were of capacities chosen so as to make the rise of temperature 

 obtained with a given specimen the most favourable for 

 accurate measurement, and were of about 4500 and 1700 cubic 

 centimetres capacity respectively. Each was provided with 

 a suitable double-walled enclosure of about ten times the 

 capacity of the calorimeter, having internal walls of brightly 

 polished metal. By tbis arrangement the temperature of the 

 jacket water, and hence the rate of rise or fall of the 

 calorimeter, could be regulated at will. A diagrammatic 

 representation of the whole arrangement is shown in fig. 1. 



Some considerable difficulty was experienced in designing 

 a suitable form of automatic release, which would free the 

 specimen at the right moment and allow it to drop vertically 

 into the calorimeter. It was found that various arrangements 

 of spring tongs which acted reasonably well at moderate 

 temperatures became unusable after exposure to the higher 

 temperatures reached in this work. The following method 

 was therefore adopted. A small loop of platinum wire, bent 

 into an open hook, was attached to the top of the specimen. 

 To two thick nickel leads was twisted a short piece of thin 

 platinum wire, the free portion between them being about 

 10 mm. long. The leans insulated from one another by 

 porcelain tubes are coupled to a key and battery, by which 

 the thin wire can be instantly fused when required. The 

 electric furnace with the specimen in position, suspended 

 from the fine platinum by means of the hook, was arranged 

 so that only a very few seconds were necessary to open the 

 lower door, swing the whole into position over the calori- 

 meter, drop the specimen, bring back the furnace and reclose. 

 Special blank experiments showed that the heat gained by 

 the calorimeter from the glowing walls of the furnace during 

 the transfer might attain, under unfavourable circumstances, 

 perhaps 2 per cent, of the amount given out by the specimen. 

 Even if some form of the ingenious tramway calorimeter 

 of Prof. Louguinine, with modifications to render it suitable 

 for high-temperature work, had been adopted, it is doubtful 

 whether this source of uncertainty would have been capable 

 of much further reduction, it may be pointed out that in 

 these experiments it is probable tbat a considerable part of 

 the uncertainty, due to the gain of heat from this source, 

 may be compensated for by the ineviiable small loss in 

 transference of the specimen from the interior of the heated 



