LUEDEKING — PHYSICO-CHEM. STUDIES IN FATTY ACID SEKIES. 639 



he used to register its temperature. After the mercury lias attained 

 its uniform temperature the slide carrying the calorimeter, whose 

 temperature has just been noted, is rapidly pushed under the stop- 

 cock of the vessel A, and in an instant a certain amount of mer- 

 cury allowed to run in ; whereupon it is at once immediately 

 withdrawn, btirred for one or two seconds, and the temperature 

 again noted. The whole of this entire operation requires at most 

 ten seconds. Then the calorimeter is again weighed and the 

 amount of mercury run in thus determined. It is appai-ent that 

 all data for calculation of the specific heat of the substance in the 

 calorimeter are then at hand. 



A very remarkable feature of the method, which is principally 

 iidopted for liquids, is, that it is so rapid of execution — by far the 

 most expeditious of any known. A single determination would 

 require at most ten minutes. Nor are there any corrections for 

 radiation to be made, since the mercury loses its heat almost 

 instantly — a fact attributable to its excellent conducting power, 

 as well as to the minute state of division in which it is showered 

 into the calorimeter. Lastly, the method is also eminently useful 

 because of its great accuracy, being but little, if any, inferior to 

 the Kopp method as modified by Bettendorf and Wiillner. The 

 method does not require much substance for a determination of 

 specific heat. From lo to 15 g. suffice, though much more may 

 be taken. Since the substance experimented on changes its 

 temperature but very little, the true specific heat between a very 

 narrow range of temperature is obtained, which is an important 

 feature. The calorimeter has usually the temperature of the sur- 

 roundings. 



The cast-iron vessel can hold mercury enough for very many 

 determinations, and thus a great number may be made in rapid 

 succession.* 



HEATS OF HYDRATION. 



Finally, I present the results of my determinations of the heats 

 of hydration of the acids of this homologous series. These meas- 

 urements were made by mixing water and acid, both of the same 

 temperature, in calorimeters of gilt brass and platinum, and of 



* The apparatus is constructed by Mr. E. Stohrer of Leipzig. 



