STIRRER. 



147 



almost instantaneous, the cover and the stirrer may be omitted, 

 and the thermometer itself employed to agitate the liquid, which 

 simplifies operations. 



Under these conditions the calorimeter is very simple, as will 

 be seen. Keduced to water it is equivalent to 3 grms. to 4 grms., 

 according to the accessory pieces, that is to say, that its calori- 

 metric mass does not exceed the two-hundredth part of the 

 mass of the aqueous liquids which it contains, a circumstance 

 which is very favourable to accuracy in experiments. 



The author has also used several other platinum calorimeters, 

 one with capacity of 1 litre, which has served for the greater 

 number of his experiments on the detonation of gases, another 

 of 2-5 litres. 



In certain experiments where it was necessary that contact 

 with the air should be completely avoided, glass phials containing 

 700 cms. to 800 cms. have been 

 used as calorimeters, always plac- 

 ing them in the same protecting 

 envelope. These instruments 

 give measurements which are the 

 more exact the larger they are, 

 but on the condition of con- 

 suming larger weights of the 

 substances. This limits the use 

 of the large instruments. On 

 the contrary, the small ones are 

 more subject to corrections for 

 cooling which may be neglected 

 with calorimeters of half a litre 

 and upwards, for the duration of 

 an ordinary experiment (one to 

 two minutes) and whenever the 

 excesses of temperature remain 

 less than 2. 



3. Stirrer. In the experiments 

 in which the stirring of the water 

 by means of the thermometer 

 was insufficient, or presented any 

 difficulty, a stirrer of special form 

 was employed, superior to those 

 hitherto used, because it more 

 completely mixes all the layers 

 of water, with less expenditure 

 of force. 



This stirrer (Fig. 20) consists of four wide helicoidal blades, 

 A A' A" A/" very thin, inclined at about 45 to the vertical and 

 normal to the internal surface of the cylinder employed as a 

 calorimeter. They are mounted on a frame formed of two 



L2 



Fig. 20. 



