NATURE AND SOURCE OF SPRAYING MATERIALS. 189 



sioii of stilt into sodium sulpluite, and (2) tiio decomposition of sodimn 

 sulphate and its conversion into sodium carbonate. The first opera- 

 tion is known as the '"salt-cake'' process, and the second as the "soda- 

 ash" process. The first step is carried out by the application of sul- 

 phuric acid to the salt and the decomposition of both in a furnace, the 

 doul)le decomposition resulting" in the formation of hydrochloric acid 

 and sodium suli)hate. The hydrochloric acid is condensed and \)ro- 

 served, while the salt is converted by heat into a hard cake of acid 

 sodium sulphate. There is usually in this cake, however, more or less 

 unaltered sodium chloride. In the second step the salt cake is pul- 

 verized and mixed with an equal weight of pulverized limestone or 

 chalk and half its weig-ht of tine coal. This mixture is heated to 

 fusion in a furnace, being constantly stirred or revolved. The com- 

 bustion of the coal under the heat which is maintained seems to con- 

 vert the sodium sulphate into sodium sulphide, and the decomposition 

 of the sodium sulphide and limestone, with the intiMchange of ele- 

 ments, produces calcium sulphide and sodium carbonate. The ivsulting 

 mass is cooled in ii'on receivers, broken up finely, and digested in tepid 

 water. The alkali dissolves and leaves the insolul)le impurities. The 

 sodimn solution is evaporated, and when dry the mass is calcined with 

 one-fourth its weight of sawdust, to more fully convert the alkali into 

 carbonate. This pi-oduct — the soda ash of commerce — is again dis- 

 solved in hot water, and the solution filtered and allowed to cool. As 

 the solution cools the carbonate of soda is deposited in large, trans- 

 parent crystals, such as are supplied to the trade. Soda ash was 

 formerly largely imported from England, but in the last few years has 

 been made in the United States to a vgyx large extent. The dissolv- 

 ing of the soda ash and the crystallizing of the sal soda is carried on 

 extensively by firms not manufacturers of the ash. A St. Louis firm 

 states that thej^ crystallize the solution of soda ash in tanks holding about 

 8,000 pounds each. After the cr3^stallization has progressed sufficiently, 

 which takes from ten to fourteen days, according to the temperature of 

 the weather, the mother Ive, which contains all the impurities, is 

 drawn off and the sal soda is then broken, dried, and packed in barrels. 

 It is stated that a newer process is to crystallize the solution in small 

 tanks, holding perhaps 200 pounds. In this small quantity the liquid 

 crystallizes in a very short time, say over night, but does not give any 

 mother lye, and consequently no impurities are removed. 



A system entirely different from the Leblanc process is in use in the 

 United States in some of the leading salt regions and has come very 

 largely into use in Europe. It is known as the ammonia soda process, 

 . or the Solvay process. It consists in decomposing a solution of com- 

 mon salt with ammonium bicarbonate, whereby the greater part of 

 the sodium is precipitated as l)icarbonate, while the anmionia remains 

 in solution as ammonium chloride. This latter salt is heated with 



