g-fS MANURES AXD MANURING 



form of thick mud is passed through the press filter if necessary and then 

 put into autoclaves and heated to a temperature of 1400 to 1500 C. This 

 temperature is maintained for 15 minutes, after which the steam exhaust 

 of the autoclave is opened, and the steam pas.sing out carries with it the 

 ammonia salts. It passes through cool condensing coils, and is then de- 

 livered into vats containing sulphuric or nitric acid for the production 

 of inodorous ammonium sulphate or nitrate. 



In the autoclave there remains a perfectl}^ dry, fine powder, ready 

 for putting up in sacks, ver}^ rich in fertilising substances and completeh' 

 sterilised. The condensation coils may, if necessary, be arranged at the bot- 

 tom of the settling basins, so as to utilise the waste heat to increase the fer- 

 mentation of the mud and produce the maximum quantity of ammonium 

 carbonate. 



The method of operation is thoroughly j^ractical and hygienic. It en- 

 sures the maximum yield and does awa^' with all the disadvantages of 

 the ordinary methods of sewage disposal. Huge distillation appliances, un- 

 healthy and repulsive smells, the expense of sterilising mixtures to be added 

 to the sewage, are all done away with, while there is a saving in supplies of 

 every kind, labour, plant and fuel, together with an increase in the agri- 

 cultural value of the manure produced. 



736 - The Solubility of " Fluospar Slag " and Mineral Phosphates in Citric Acid. — 



I. Robertson O. S. The Influence of Fluospar on the Solubility of Basic Slag in Citric 

 Acid. — Journal of the Society of Chemical Industry, Vol. XXXV, No. 4, pp. 216-217. I,on- 

 tlon, igi6. — II. Ibid. The Solubility of Mineral Phosphates in Citric Acid, Part II (i). — 

 Ibid., pp. 217-220. 



I. — During the past few years British steel manufacturers, particularly 

 those using the basic open hearth process, have been introducing flitorspar 

 into the furnace. Fluorspar produces a much more fusible slag and greater 

 quantities of lime can therefore be added without making the slag too thick. 

 Many thousands of tons of this "fluorspar slag" are produced annualh 

 and form a waste product ; one Teeside firm alone produces over 100 000 

 tons per annum ; certain firms even pay a few pence per ton to have the 

 slag carried out to sea. 



The peculiarity of basic slag produced b}" the use of fluorspar is that 

 the solubilit}- of the phosphate, according to the citric acid test, varies from 

 20-50% instead of from 70-90%. 



Original " fluorspar slags," artificially prepared " fluorspar slags " 

 and Tunisian rock phosphate were subjected to five consecutive half-hour- 

 extractions with 500 cc. of 2 per cent citric acid. The results clearly show 

 that the citric acid test gives no true idea of the solubility of the phos- 

 phate in " fluor-spar slags " and affords no guide to its value to the plant. 



The use of fluorspar in the manufacture of steel b}^ the open hearth 

 process results in the production of a phosphatic slag with low citric sol- 

 ubility. 



Nevertheless the slag is completely soluble in citric acid if sufficient 



(i; Parti, see Z>'. March 1914, Xo. 214. {Ed.). 



