104 MESSRS. WALTER ROSENHAIN AND P. A. TUCKER. 



100 C. By means of a thin wire attached to the specimen, this was then lowered 

 into a large Dewar vessel containing a moderate quantity of liquid air ; the specimen 

 hung just above the surface of the liquid air, the mouth of the vessel being loosely 

 stuffed with cotton-wool in the usual manner. Thus arranged, the specimens, 

 weighing about 200 grammes, were found to cool at a convenient rate, and inverse- 

 rate observations could readily be taken. Heating- curves were obtained by removing 

 the specimen from the Dewar vessel, having first immersed it in the liquid air so as to 

 ensure the attainment of the temperature of boiling liquid air ( 189 C.). If the 

 specimens were simply allowed to warm in the air of the room the process was found 

 to be inconveniently slow, while the heating-curve could not be carried up to the 

 ordinary temperature ; the specimens were therefore hung up in a vertical metal 

 cylinder placed above a previously warmed crucible ; this arrangement gave a 

 convenient rate of heating, and allowed the observations to be carried well above the 

 ordinary temperature. One inconvenience arose, however, from the formation of rime 

 (ice) on the surfaces of the specimens as soon as they were removed from the liquid- 

 air vessel ; when the temperature C. was reached, the melting of this ice caused an 

 arrest in the rate of heating which might have masked an arrest due to the alloys 

 themselves, but the observation of the corresponding cooling-curve serves to remove 

 this doubt. Typical examples of the curves obtained in this way are given in fig. 8, 

 and it will be seen at once that they contain no indication of any evolution (or 

 absorption) of heat at low temperatures in these alloys. It follows, therefore, that 

 the transformation to which these evolutions of heat are due does not occur in alloys 

 containing less than 8 per cent, of tin. 



The above conclusion is further borne out by a consideration of the approximate 

 quantitative interpretation of the curves already described. TAMMANN* has pointed 

 out that the determination of the quantity of heat generated in a recalescence, 

 whether it arises from the solidification of a eutectic or from transformations in the 

 solid, may yield valuable information as to the constitution of a series of alloys. On 

 the other hand, the present author has recently discussedt the theory and interpre- 

 tation of cooling- curves, and has shown that any strictly accurate quantitative 

 interpretation of the areas of the peaks on inverse-rate or derived differential cooling- 

 curves in terms of quantities of heat is not possible, at the same time indicating the 

 manner in which rough approximations may be obtained. The results now to be 

 quoted must therefore be read with all the limitations which apply to such approxi- 

 mations, but even with these limitations they appear to yield some interesting results. 



Apart from errors introduced by variations in the mass of the cooling body and in 

 its specific heat, and by variations in the rate of cooling, it has been shown in the 

 paper cited above that the areas of the peaks of inverse-rate and of derived differ- 

 ential curves represent the quantities of heat generated by the recalescences in 



* ' Zeitschr. Anorg. Chem.,' 37 (1903), p. 303 ; 45 (1905), p. 24 ; 47 (1905), p. 299. 

 t Paper cited above. 



