20 



hydrogen fluoride is condensed in the receiver cooled with ice and 

 salt. The liquid is then introduced into the U-tube cooled with 

 methyl chloride boiling at 23 and subjected to the action of a 

 current from 20 large Bunsen's elements coupled in series. Any 

 small quantity of water present is decomposed with liberation of 

 ozone at the positive pole, but as the water disappears the 

 resistance increases rapidly, until, when the hydrogen fluoride is 

 perfectly pure, a current from even 25 cells no longer passes. 

 To obtain the necessary conductivity, a small quantity of 

 perfectly dry potassium hydrogen fluoride is dissolved in the 

 liquid. Under these conditions hydrogen is given off at the 

 negative pole, whilst at the positive pole a gas is evolved in 

 which crystallized silicon, adamantine boron, arsenic, antimony, 

 sulphur, and iodine take fire spontaneously. 

 This gas is fluorine 



104. Bunsen's absorptiometer. 



E. 220. 1877. Made by G. Desaga, Heidelberg. 



This apparatus is used for the determination of the absorption of 

 the more insoluble gases. The absorption tube within the large 

 tube is divided into millimeters and accurately calibrated, it has 

 a small iron band furnished with a screw, luted on its lower and 

 open end, this fits into another screw attached to a small iron 

 stand with a plate of caoutchouc covering the bottom. By this 

 means the open end can be screwed down on the plate, and the 

 tube thus completely closed. Two grooves on each side of the 

 stand permit of a sliding movement on two vertical pieces on 

 the foot of the apparatus inside the glass tube, so that the small 

 iron stand can be raised or depressed, but not turned horizontally 

 on its axis. 



The outer glass tube is provided with ground glass edges at 

 the bottom end, which can be pressed against caoutchouc rings 

 inserted in the foot and in the rim, by means of the two nuts at 

 each side of the top of the apparatus, working on screws on the 

 two vertical side rods. The tube at the side is for pouring in 

 mercury, a cock being provided for letting it out, so that any 

 desired pressure is obtained in the absorption tube by raising or 

 depressing the level of the mercury in the inner glass cylinder. 

 The temperature of the surrounding water is determined by a 

 thermometer placed in the outer tube. The upper end of the 

 large glass tube is closed by an iron lid, hinged at one side and 

 fastened down by the nut and screw. The tube is rendered 

 water-tight by a band of caoutchouc inside the lid. 



The absorption tube is filled with mercury at the trough, and 

 a quantity of gas passed into it. The volume of the gas is 

 determined with all due precautions. A quantity of water per- 

 fectly free from air is passed up into the tube, which is then 



