BORON AND FLUORINE. 15 



plate of asbestos board (not shown in the sketch) covered with 

 sheet nickel. Noxious vapors could be removed by a small hood 

 placed over the part of the apparatus which projected above the 

 asbestos board. This hood consisted of two well-fitting, over- 

 lapping cylindrical shells of sheet copper which, when in position, 

 formed a complete cylinder. The latter was capped by a platinum 

 funnel, the stem of which could be connected to an exhaust. A 

 vertical slot, in the side of the cylinder, served for the introduc- 

 tion of a thermometer, or pyrometer, to roughly measure the 

 temperature within the air-bath. In the stronger ignitions, such 

 as were necessary in fusing the salts, the asbestos board was dis- 

 pensed with; but the bulb was protected by a crucible, which in 

 this case rested on a triangle and could be covered with a platinum 

 lid consisting of two overlapping sections. In this manner the 

 heat was concentrated on the bulb proper without overheating 

 the neck. 



The current of air which passed through the apparatus during 

 an experiment was produced by a water blast. Before reaching 

 the pump the air was drawn through a solution of caustic soda. 

 It was then conducted through a solution of potassium perman- 

 ganate containing potassium hydroxide, and next through moist 

 soda-lime, fused caustic potash, concentrated sulphuric acid, and 

 finally, before reaching the platinum combustion tube, through a 

 tower filled with freshly fused caustic potash. The train was 

 constructed entirely of glass. The plug of the combustion tube 

 was provided with a platinum inlet tube which was joined to the 

 glass train by means of a "glass spring," the free end of which 

 was ground into the metal tube. 



THE DEHYDRATION OF BORAX. 



For obvious reasons it seemed desirable to refer the analyses 

 of borax to the anhydrous salt. It was found, however, that the 

 complete expulsion of water from borax is no simple matter. The 

 observations of Dobrovolsky in 1869, concerning the dehydration 

 of this salt, seem to have attracted no attention until they were 

 mentioned by Brauner in 1906. 10 According to Dobrovolsky only 

 email quantities (0.1 to 0.3 gram) of borax can be dehydrated 

 completely, whereas larger quantities retain water. 



. 



In Abegg's Handbuch d. anorg. Chem., Vol. Ill, part 1, p. 6. 



