318 LECTURES TO SCIENCE TEACHERS. 



that the dilute acid which I have thus prepared is now 

 turbid, and this is caused by the separation of insoluble 

 sulphate of lead, which was held in solution, and was 

 therefore invisible in the strong acid. 



The hot acid is then run off from the concentrating pans 

 into a leaden trough surrounded by cold water, whence it 

 passes into reservoirs or carboys. In this form the acid is 

 technically known as B.O.Y., or brown oil of vitriol, as 

 it is always slightly coloured from the presence of traces of 

 organic matter. In this condition it is very largely sold 

 for a great variety of purposes. 



In order to concentrate the acid still further, and to drive 

 off all the water which it contains, the concentrated oil of 

 vitriol must be heated in vessels of either glass or platinum, 

 substances which are not attacked by hot sulphuric acid of 

 any degree of strength. In England glass vessels are most 

 usually employed, whilst on the Continent platinum rectify- 

 ing plant is more common. The glass vessels or retorts in 

 which the acid is rectified are large, well-annealed, and 

 evenly-blown vessels, capable of holding twenty gallons of 

 the acid. Each retort is placed on an iron sand-bath, under 

 which is a fire, so arranged, however, that the flame does 

 not touch the retort. The acid having been heated in these 

 retorts until all the water is driven off, is allowed to cool, 

 and then drawn off into carboys. This is termed rectified 

 acid. A very beautiful and quite novel arrangement for 

 rectifying oil of vitriol in platinum is exhibited by Messrs. 

 Johnson, Matthey, & Co. By means of this arrangement all 

 evaporation of the acid in leaden pans is avoided, and thus 

 the operation is not only cheapened, but the acid obtained is 

 nearly free from lead. The new arrangement consists of 

 two pans made of corrugated plates of platinum, and heated 

 by a fire ; at one end of these the chamber acid is allowed 

 to run in a thin stream, whilst at the other a continuous 

 stream of concentrated acid is obtained. For the purpose 

 of completing the rectification the acid flows into a retort 

 also of platinum having a corrugated surface, and then the 

 perfectly strong acid runs out through a platinum worm 

 into the glass carboy in which it is sent to market. 



We may next ask, Is the usual working of the chambers 

 in England as good as it can be 1 In answer to this I may 

 reply that as a general rule a yield of 290 parts of pure 



