Lyons — Volume Change on Fusion. 6.9 



meter allows the substance to be introduced in tlie liquid state with the 

 greatest facility, and also renders easy the sealing of the bulb. The precision 

 of the method, as estimated by the possible errors due to observation, may be 

 illustrated by the following exnmple : — In the examination of bees' wax, the 

 mass of mercury required to fill the bulb was about 36 grammes, and a, the 

 mass required to fill one centimetre of stem, = •0357 grms. It was found that 

 at 70° C. an observational error of 1 ram. in reading R would liave made the 

 value of F = ri929 instead of 1'1930. It was quite easy to read R correct 

 to -fV m™- > fiii^ ^s the weighings might be carried if necessary to four decimal 

 places, the final results might be regarded as correct to this degree in the 

 absence of any constant or systematic sources of error. 



The chief and practically the only source of systematic error is the efl'ect 

 of variation of external or internal pressure on the volume of the bulb. 

 When the bidb is cylindrical and strong, the effect of pressure must be very 

 slight, and in most cases negligible. If the bulb be of the flat form, and 

 thin -walled, the conditions of internal pressure being very approximately the 

 same when the bulb is filled with mercury as when it contains the substance 

 in the liquid state ; the errors due to the pressure effect will be extremely 

 small in the final results. When, however, the substance solidifies, it might, 

 under certain conditions, cause abnormal internal pressure effects ; but in the 

 case of waxes a little below their melting-points, such effects are not likely to 

 arise owing to the continued plasticity of the substance. As to the external 

 pressure and its variation with the barometer and depth, corrections may be 

 applied in the manner adopted in accurate thermometry. Such corrections 

 would only be necessary in cases of extreme accuracy. 



Examination of some Waxes. 



To illustrate the application of the method to the study of solid fats and 

 waxes, the following results, obtained for three samples of wax, are given. 

 The samples consisted of (1) what may be regarded as genuine yellow Bees' 

 Wax ; (2) what is referred to as " White Wax" ; and (3) a mixture composed 

 of one part of the former to two of the latter by weight. The " White Wax " 

 was purchased in plates as " Cera Alba, B.P.," but as it differed in its density, 

 melting-point, and refractometer index from the values quoted for the B.P. 

 wax, it is, in consequence, referred to here as " White Wax " rather than 

 " Cera Alba." Tlie values of the volumes of one gramme and the density are 

 given in the accompanying tabular statement, and the former are graphically 

 represented in fig. 2. 



The appearances in the bulb were carefully noted during the period of 

 fusion, and were found to correspond to marked changes in the form of the 



