TECHNICAL CHEMISTRY. 333 



Dr. C. K. A. Wright has made a series of experiments on 

 the loss of soda occurring in the black-ash process. He 

 believes the loss to be as follows : 



Sodium salt undecomposed ... 3'49 per cent. 



Sodium compounds rendered insoluble 5 '44 ,, 

 Sodium compounds vaporized 1'14 ,, 



10-07 



The next branch of the soda manufacture to which I 

 must direct your attention is that of the preparation of 

 soda crystals or washing soda (Na 2 C0 3 + 10H 2 O). For this 

 purpose a warm saturated solution of carbonate of soda is 

 allowed to stand for some weeks in large tanks. The 

 crystals are gradually deposited and frequently grow to a 

 very large size. The mother-liquor is then run oil, and the 

 mass of solid crystals broken up for market. 



Bicarbonate of soda (NaHCO 3 ) is the next product. This 

 is largely used in medicine, as also in the preparation of 

 baking-powders, effervescing powders, and drinks. It is 

 made by simply exposing crystalline masses of the ten-atom 

 hydrate to the action of carbonic acid gas generated from 

 limestone. This gas is greedily absorbed by the crystals, 

 which lose their water of crystallization, and with it their 

 transparency, 



NasCOg, lOHoO + C0 2 - 21SraHC0 3 + 9H 2 (X 



The production of solid caustic soda has lately become 

 an important branch of the alkali industry. I have already 

 stated that the black-ash liquors contain a considerable 

 quantity of caustic soda. When the black-ash crystals 

 separate out, a mother-liquor, to which the name of red- 

 liquor is given, is left behind, containing the whole of this 

 caustic soda, and this is now largely used for the production 

 of solid caustic alkali. For this purpose, however, the 

 carbonate of soda, which is likewise contained in solution 

 in the red-liquor, must be causticized, and this is done by 

 reducing the strength of the liquor from specific gravity 

 1'28 to specific gravity I'lO, and then boiling this by means 

 of steam with milk of lime, the reaction which occurs 

 being : 



Na 2 C0 3 + Ca(OH) 2 = 2NaOH + CaCO 3 . 



