=—_” 
a 2 eee 
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= ae 
TRANSACTIONS OF SECTION B. 985 
its freshness, the sodium aluminate may be precipitated with aluminium sulphate, 
when the following reaction takes place :— 
3Na,A1,0, + Al,(SO,),18H,O = 
3Na,SO, + 4A1,(HO), + 6H,0. 
Indeed as the decomposition of the insoluble aluminate formed only takes place 
slowly, it is best to use this method in addition, even when adding the aluminate 
alone for softening, in all cases where much organic matter is present which it is 
desired to get rid of, and thus it is very applicable to the purification of sewage, 
waste waters from factories, &c. Its advantages consist— 
(1) In its economy over every other known method of precipitation by alu- 
minium hydroxide. 
(2) The comparatively harmless nature and small proportion of the salt left 
in solution. 
The usual way of obtaining the hydroxide is by aluminium sulphate and lime 
or chalk. But the sulphate (even the pure crystallised salt) contains only 15:44 
per cent. of alumina (the commercial salt about 2 per cent. less), while sodium 
aluminate contains 523 to 623 per cent. and even the crude salt of commerce 
now obtainable abroad 33 per cent., so that a very much smaller quantity of the 
latter will suffice to produce a given quantity of hydroxide. Again, by using the 
sulphate with any salt other than the aluminate, the quantity of matter left in solu- 
tion would be greatly increased, while in the case of lime or chalk with sulphate 
the effluent would possess that objectionable quality, ‘ permanent hardness.’ 
As to the question of cost, sodium aluminate has never been manufactured in 
England on a large scale, so that its price at present is abnormally high, though 
there is reason to believe that ere long it will fall considerably. As it is, where 
water possesses 20 degrees of hardness—7e., 10 permanent and 10 temporary—it can 
be freed from both these, as well as from any organic matter, for about 2d. per 1;000 
gallons. Practically, and using the crude salt, the expenditure in the above case 
would be only just over 1 grain per gallon and per degree of hardness. The simple 
purification of water or sewage would be considerably less, 
Tn experimenting practically with the above process for purifying sewage and 
waste waters it must be borne in mind, first, that great care must be taken to 
obtain a proper aluminate; and, secondly, that the salt should not be previously 
dissolyed, but added, finely powdered, to the liquid it is desired to purify. 
TUESDAY, SEPTEMBER 15. 
The following Reports and Papers were read :— 
1. Report on Vapour Pressures and Refractive Indices of Salt Solutions. 
See Reports, p. 284. 
2. Report on certain Physical Constants of Solution.—See Reports, p. 261. 
3. On Solutions of Ozone and the Chemical Actions of Liquid Oxygen. 
By Professor Drwar, F.R.S. 
4. On Physical Molecular Equivalents.!. By Professor Gururin, F.R.S. 
1 Published in the Chemical Nen's, 1885. 
