466 Scientific Proceedings, Royal Dublin Society. 



nitric acid. This quantity of solution contained about 2-4 x 10"' gram of 

 arsenic. If it be assumed that this was all sublimed as arsenious oxide, the 

 sublimate must have consisted of about 3 X 10"' gram of matter, and was 

 deposited to an average thickness of about 2 x 10"^ cm. While it would be 

 impossible to identify deposits in such vanishingly small amounts, yet in a 

 sublimate from about 10"^ gram of arsenic in 'solution, the " pupil " of un- 

 oxidized arsenic in the centre was just visible. 



The foregoing process would be an excellent method of obtaining a thin 

 film of matter in a high state of purity. 



Summary. 



1. The method of analysis described above possesses a range of action 

 enormously superior to tliat attained by the blowpipe, and limited only by 

 the volatility of the carbon, and hence is capable of revealing effects 

 impossible to obtain in blowpipe work. 



2. It is possible to examine the effect of heat upon substances in 

 different atmospheres, sublimates being formed with the same facility in 

 these atmosplieres as they are in air. These processes would be by ordinary 

 laboratory methods very laborious, if not impossible. A mineral powder may 

 in the course of a few minutes be strongly heated in hydrogen, oxygen, 

 sulphuretted hydrogen, hydrogeu chloride, nitrogen, or other atmosphere, 

 with the deposition of various distinctive sublimates. 



3. Mixtures or alloys, such as brass, or even steel, may be dealt with to a 

 certain extent by means of fractional volatilization, the deposits produced 

 being removed on separate cover-glasses. Even when no attempt is made 

 at fractionation, sublimates tend to become automatically separated ; those 

 of greatest volatility sublime first, being seen through a glass cover-plate, 

 whilst the more refractory substances sublime last, and are seen under 

 the plate. Yery small quantities of impurities in metals have been 

 thus detected, the cadmium present in commercial zinc being easily 

 distinguishable. 



4. Experiments being made under couditions of cleanliness and with 

 small chance of loss, tests may be carried out on smaller quantities of 

 material than would be otherwise possible. 



IvEAGH Geological Laboeatory, 



Trinity College, Dublin, 



26ife November, 1912. 



