( 94) 



However, at last, I succeeded in getting a satisfactory coating of 

 the surface by substituting for white wax the ordinary, yellow 

 bees-wax. This contains an adhesive substance probably derived 

 from the honey, and, when mixed in the proper proportion with 

 elaidic acid it yields the desired surface coating. 



I have also coated ^) the bottoms of the plate and the sides, except 

 those which stand J_ on the line of demarcation with a thick layer 

 of varnish mixed with mercury iodide and copper iodide. During the 

 operation the heating was continued to incipient darkening (about 70'). 



The plates should have a rectangular or square form, as otherwise 

 the isotherms generall}' become curved. 



It is further essential to heat rapldh/ and to raise the copper bolt 

 to a fairly high temperature; the isotherms then possess a more 

 straight form and give more constant values for f. 



I executed the measurements on the double object table of a 

 Lehmann's crystallisation microscope on an object glass wrapped in 

 thick washleather, to prevent the too rapid cooling and solidification 

 of the coating. 



After numerous failures, I succeeded at last in obtaining a long 

 series of constant values As the mean of 30 observations, I found 

 f = 22^12' and therefore: 



- = 1,489. 



Ac 



§ 6. The value now found is somewhat greater than that found 

 by Perrot. I thought it would be interesting to find out in how 

 far a similar deviation was present in other cases, and whether when 

 compared with the results obtained by the methods of Senarmont, 

 Janettaz and Roentgen, it has always the same direction. 



In fact, the investigation of many minerals has shown me that 

 all values obtained previously, are smaller than those obtained by 

 the process described here. 



I was inclined at first to believe that these diiferences were still 

 greater than those which are communicated here. Although a more 

 extended research, including some plates kindly lent to me by Prof. 

 VoiGT, showed that these ditferences are not so serious as I suspected, 

 at first the deviation exists ahimys in the same direction. 



For instance, I measured the angle « of a plate of an Apatite- 

 cry stsd from Stillup in Tyrol and found this to be 17°. From the 



') RicHARz's method of experimenting (Nalurw. Rundschau, 17, 478 (1902)) did 

 not give sufficiently sharply defined isotherms and was therefore not applied. 



