c«nti|it Jims 



FOR GENERAL READERS. 



Vol. I. — No. 20. {New Series.) 



FRIDAY, MAY iSth, i£ 



rWeekly, Price ! 

 I By Post.. 3}d. 



CONTENTS. 



Current Events 



Scientific Table Talk 



A Disappearing Gun Turret (illus.) 



Soil and Soil Makers ... 



Apparatus for Generating Carbonic 



Acid Gas (illus.) 

 New Thermograph of the Royal Ob- 

 servatory, Greenwich (illus.') 

 Photographic Lenses ... 

 General 5fotes ... 



The Canine Teeth of JIan [illus.) ... 

 The Storm at Dacca ... 

 Natural History : 



Fish Culture {illus.) 



The Growth of Plants 



PAGE 



Edinburgh Geological Society ... 475 



Dundee Naturalists' Society ... 476 



Correspondence : 



Red Snow {illus.) — British 

 Lichens — Meteoric Stones — 



The Ichthyosaurus ... ... 476 



Answers to Correspondents ... ... 477 



Recent Inventions 477 



Technical I'Mucation Notes 478 



Announcements ... ... ... 479 



Diary for Next Week 479 



Sales and E.xchanges ... ... ... 480 



Selected Books... ... ... ... 480 



Meteorological Returns ... ... 480 



The Chehical Treatment op Sewage. — The Man- 

 chester Guardian has pubHshed a resume of Sir Henry 

 Roscoe's recent report on deodorising London sewage. 

 As to the use of chemicals, he reminds us that it can 

 only be regarded as an expedient for deodorising, and 

 for initiating a process of purification. With so enormous 

 a bulk as that of the Metropolitan sewage, no quantity of 

 chemicals can be added which is sufficient to change the 

 whole of the solid matter into a harmless substance. 

 The problem therefore is a very difficult one, seeing that 

 a treatment to be thoroughly efficient must not only get 

 rid of bad smells, but must maintain the wholesomeness 

 of the river into which the sewage is eventually dis- 

 charged. Sir Henry Roscoe has been inaking various 

 experiments, and in his report he points out that amongst 

 natural processes the most important is the change pro- 

 duced by living organisms. This change is twofold, one 

 being due to the action of organisms requiring free 

 oxygen for their growth, with the result that the organic 

 matter is rendered inoffensive — the other being due to 

 the organisms which thrive in the absence of free oxygen, 

 and give rise to offensive products. The difficulty is to 

 preserve the " healthy " organisms, while preventing the 

 growth of those yielding offensive exhalations. 



Apparently, the practical difficulty is to find a sub- 

 stance or fluid which will supply oxygen enough to the 

 sewage to prevent its putrefaction ; but in reality the 

 difficulty is even greater. River water unpolluted holds 

 in solution oxygen from the air, and is therefore a useful 

 oxidising agent, but, as Sir Henry Roscoe says, the 

 sewage on its way to the outfall undergoes a change of a 

 putrescent character, owing to the growth of the 

 " unhealthy " organisms. The products of this putre- 

 factive change readily absorb free oxygen, so that when 

 they pass into the river they deprive it of its dissolved 

 oxygen, and the " healthy." growths cannot take place. If 



deodorants are added, the putrefying substances are 

 removed by oxidation, but the treatment is far from being 

 complete unless the deodorised sewage is brought in 

 contact with the free oxygen which is necessary for the 

 growth of the " healthy " organisms. It will thus be seen 

 how complex and difficult are the conditions to be filled, 

 and how essential it is that the subject should be investi- 

 gated in a thoroughly scientific manner. Large sums of 

 money have been spent lavishly, if not wastefully, by the 

 Metropolitan Board of Works, in treating the sewage 

 chemically at the outfall works, and it is now made 

 abundantly clear that this can have no other result than 

 to render the sewage less oifensive in smell. It in no 

 way prevents the pollution of the water, and it is of the 

 utmost importance that means should be devised for 

 effecting this. Sir Henry Roscoe seems to think it may 

 be done by aerating the sewage before it enters the river, 

 as the cost of pumping in air need not be great. 



Domestic Electric Lighting.— Notwithstanding the 

 fact that lighting by electric glow lamps is usually more 

 expensive than by ordinary lighting gas, the number of 

 the former now in use is considerable. Mr. Swan stated 

 the other day that in London alone about .'■50,000 are 

 lighted up every day. We believe that the number sup- 

 plied from the Grosvenor Gallery electrical station has now 

 grown to something like 20,000, and that there is every 

 probability of the number being farther increased. The 

 Cadogan Coiupany have made a fair beginning, and we 

 learn that the Kensington Court Company find it neces- 

 sary to double their generating power to meet the 

 increasing demands of the neighbourhood. We are glad 

 to notice this extended use of the electric glow lamps, not 

 only because they give a steady light without vitiating 

 the air, but because there is nothing like actual ex- 



