588 Professor Sir James Deicar '" [March 25, 



the graduated receiver F. Immediately preceding or following this 

 observation, a similar experiment is made with a small portion of a 

 selected standard substance, namely, lead. The quantity of lead is so 

 chosen as to produce about the same volume of .sras in the receiver as 

 that supplied by the portion of substance experimented on. By this 

 means, the circumstances of the two observations are made as similar 

 as possible, and thereby many sources of error are eliminated. 



When the hydrogen calorimeter is to be used, the temperature 

 being so much lower than in the liquid-air cal jrimeter, we have to 

 keep the ordinary atmosphere from entering the mouth of the tube 

 G by means of a current of hydrogen. This is attained in the man- 

 ner shown in Fig. 3. An ordinary Kipp apparatus A supplies hydro- 

 gen which, after being dried in the U-tube B, is allowed to pass by 

 the stop-cock C to the calorimeter D and tube E. The hydrogen 

 passes continually through the apparatus until the moment of begin- 

 ning an experiment, when the stopcock C is turned and the hydrogen 

 cut off. 



In Fig. 4 are show^n various forms of calorimeters which were 

 experimented with in determining the best form for the calorimeter 

 bulb. The final form adopted was that shown in D, Fig. 4. Stray 

 globules of the liquid hydrogen might splash up on dropping the 

 substances to be experimented on into the calorimeter, and get 

 carried over into the gas receiver, but this cause of error was found 

 to \)Q negligible, provided the calorimeter was large enough. 



When the body has to be transferred from solid carbonic acid or 

 liquid air to the calorimeter, the following procedure is adopted. It 

 is placed in the small test tube, above the indiarubber joint, which is 

 inserted into a small vacuum vessel containing some of the substance 

 (solid carbonic acid or liquid air), so that at the moment of making 

 the experiment the solid, by a quick vertical movement of the vacuum 

 vessel, is thrown into the calorimeter. A little cotton wool inserted 

 in the mouth of the vacuum vessel prevents the carbonic acid paste, 

 or liquid air, from being ejected. 



Observations were made to determine what allowance bad to be 

 made for loss of heat while the small body was falling down the 

 tube B ; also for similar losses by impacts on the sides of the india- 

 rubber joint and of the glass tube. The substances used were lead, 

 diamond, and graphite, and as the errors in any case did not exceed 

 one-half to two-thirds per cent., they may in general be neglected. 



The calorimeter may be put to various uses. Thus, on pass- 

 ing down the tube of the calorimeter wires of copper, iron, and 

 german-silver, and noting the different rates at which the gas is 

 evolved, we see that it is about six times more rapid with copper than 

 with iron, and nine times more rapid than with german-silver, 

 while with small rods of glass or ebonite no gas is produced in a 

 short period of time. Again, we may measure the heat given up by 

 1 condensation. Thus, if a small bulb containing some carbonic acid 



