514 SEC. 13. CHEMISTRY. 



III. MODELS, DIAGRAMS, APPARATUS, AND PRO- 

 DUCTS USED IN THE TEACHING OF TECHNICAL 

 CHEMISTRY. 



2459. Spence's Process for the Manufacture of Alum. 



Specimens to illustrate the process, consisting of : 



(1.) Shale of the coal measures before calcination (source of 

 alumina). 



(la.) Shale after calcination. 



(2.) Pyrites or bi-sulphide of iron (source of sulphur for the 

 manufacture of sulphuric acid). 



(2.) Nitrate of soda, for oxidising the sulphurous acid pro- 

 duced from the pyrites into sulphuric acid. 



(2b.) Sulphuric acid, specific gravity 1*6, as used in the manu- 

 facture of alum. 



(3.) Gas liquor (source of ammonia). 



(3.) Sulphate of ammonia. 

 Sulphate of alumina. 



[5.) Fish crystals of ammonia alum (a double salt or compound 

 of sulphate of ammonia and sulphate of alumina). 



(6.) Ammonia alum. Second crystallisation. Peter Spence. 



2460. Oxalic Acid. Two specimens. One crystallised from 

 a solution containing sulphuric acid, the other from an aqueous 

 solution. Roberts, Dale, fy Co. 



This product is made by the action of caustic potash, or a mixture of 

 caustic potash and caustic soda on woody fibre (sawdust). The result of this 

 action is oxalate of potash. The oxalic acid is isolated by precipitation as 

 oxalate of lime, and the subsequent decomposition of this latter product by 

 sulphuric acid. Specimen No. 2 is crystallised from water. A comparison 

 will show the marked difference in crystalline form due to the presence of 

 sulphuric acid. 



2461. Binoxalate of Potash. Roberts, Dale, $ Co. 



2462. Deacon's Apparatus for exposing porous materials 

 and currents of gases to mutual action. Sectional working model, 

 illustrating the application of one form of the apparatus to 

 Deacon's process for producing chlorine. Henry Deacon. 



In this example, the layer or " wall " is vertical and circular, and forms a 

 section of a cylinder. The frames resemble those of Venetian blinds, with 

 the laths inclined at an angle of 45, and so far apart, that an imaginary line 

 joining the upper edge of each lath and the lower edge of the one above it 

 is more horizontal than the natural angle of repose of the porous material 

 itself, which is thus retained and supported by each lath in succession. A 

 " wall " of this kind on being raised in height adds to the pressure on the 

 bottom layers only so long as the height is less than that of a cone whose 

 base is the width of the " wall," and whose sides are at the same angle as the 

 natural angle of repose of the material. This increase of pressure diminishes 



