TRANSACTIONS OF SECTION B. 535 



from that process, and by the use of a solution of alumina to effect its complete 

 purification. 



In operating upon this clarified lime-eflSuent, I find two great advantages, i he 

 first of these is that the effluent always contains a portion of lime in solution 

 eutficient to decompose the small quantity of aluminous salt which is required. 

 When this salt is added, the lime-effluent, invariably opalescent, generally 

 coloured, and never transparent, at once changes its appearance, the alumma in 

 precipitating unites Avith the albumen and colouring matters, and in a few minutes 

 coagulates and slowly descends, leaving the fluid transparent, colom-less, and free 

 from smell, this effluent or water being now fit for any purpose except potable 



uses. . . 



The second advantage of this new process is that the precipitate which con- 

 tains all the alumina of the salt used settles to the bottom of the tanks as a light 

 flocculent body, and can from thence be pumped up into suitable reservoirs, and 

 when we add to it the equivalent quantity of sulphuric or hydrocliloric acids re- 

 qiusite for combination, then in the cold and however largely diluted, all the 

 alumina is dissolved, and the same quantity of aluminous salt in solution is formed 

 as was originally used, and after allowing the very small quantity of coloured 

 albuminous residuum to subside, the solution is run into a new quantity of lime 

 effluent, thus using the alumina over and over again, and reducing the cost of the 

 aluminous compound to that of the cost of the acid needful for its resolution. 



I have fully verified the facts that all the alumina is in these circumstances 

 thro-^vn down, and that when so precipitated it is again all dissolved without using 

 any excess of acid. 



The cost of the process is thus reduced to a very small sum when compared 

 with any mode of purifying now in use. WhUe nearly all the modes which really 

 purify are impracticable, the new plan only requires a small extension of the 

 apparatus where lime-clarification is adopted, and. that process has come largely 

 into use on the ground of its cheapness, while it is only a mitigation of a great 

 evil, yet its cost is not less than 50s. to 70s. for every million of gallons operated 

 upon, and some of those who are now doing their best with it are threatened with 

 prosecution and probably injunction. 



If the new process in such cases were added to it, I estimate that it would not 

 add more than one-fifth to their expenses, and I have no hesitation in giving the 

 assurance that nothing else in sewage-purification will be required when the plan 

 now proposed is fuUy carried out. 



SATURDAY, AUGUST 28. 



The Section did not meet. 



MONDAYy AUGUST iO. 

 The following Papers were read : — 



1. On the Befraction-equivalent of Diamond and the Carbon Compounds. 

 By J. H. Gladstone, Ph.D., F.B.S. 



It was shown by Mr. Dale and the author, in 1863 (' Phil. Trans.' p. 317), tha. 

 the specific refractive energy of a substance was a very important property ; for it is 

 a constant, little, if at all, affected by changes of temperature, of aggregate condition 



