LABORATORIES FOR SPECIAL PURPOSES 57 



escape of corrosive gases from alkali works, vitriol and glass 

 works. The gases allowed to pass up the chimney with the 

 smoke, and thus to escape into the atmosphere, are required to 

 contain in one cubic foot not more than grain of muriatic acid, 

 and from vitriol works the sulphurous and nitrous gases are not 

 permitted to produce an acidity corresponding to more than 

 4 grains of anhydrous sulphuric acid per cubic foot before ad- 

 mixture with the air or smoke which passes into the atmosphere. 

 Tests of this kind require to be made either continuously or at 

 frequent intervals. 



Another kind of chimney test which is adopted in many 

 works involves the analysis of the gases passing up a flue con- 

 nected with furnaces, with the object of regulating the com- 

 bustion. Here samples of the gas are drawn from the flue, and 

 a measured volume is passed through an apparatus where, in 

 successive vessels, the constituents of the gas are absorbed and 

 measured. The carbon dioxide is absorbed by caustic potash, 

 the oxygen by phosphorus, the carbonic oxide by an ammoniacal 

 solution of cuprous chloride, while the nitrogen remains. Other 

 gases would have to be provided for by appropriate reagents. 



As an example of the tests which have to be applied in order to 

 check the progress of a manufacturing operation the case of 

 phosphorus in steel may be quoted. When phosphoric ores are 

 used the pig-iron made contains the phosphorus, and to eliminate 

 this in the production of steel from iron of this kind the basic 

 process is employed. When the operation in the Bessemer or 

 other furnace is supposed to be complete a sample of the fluid 

 metal is taken, plunged into water to cool it, and some borings 

 are immediately obtained, these are dissolved in acid, the 

 phosphorus is precipitated in the form of phospho-molybdate, 

 which is collected, dried, and weighed. From the weight of this 

 precipitate, by reference to a table, the amount of phosphorus 

 present in the sample is known. As the furnace is waiting with 

 the charge of molten steel in it, these operations from first to 

 last must be accomplished in a very short time, usually less than 

 half an hour. 



Raw materials must be analysed not only because they are 

 commonly bought according to a specification as to quality, but 

 their treatment by the manufacturer depends in many cases on 

 the amount present of some one constituent or the percentage 

 of one or other of several impurities. Thus the soap-maker 



