BY THE HON. W. F. TAYLOR M.D., ETC. 41 



(1.) Exjwsure to the air in divided currents removes hydrogen 

 sulphide, offensive organic vapours, and possibly dissolved 

 organic matter. 



(2.) Boilini/ and agitation. — This plan gets rid of calcium 

 carbonate, iron in part, hydrogen sulphide, and lessens organic 

 matter. It also destroys parasites and bacterial organisms, and 

 is on the whole the safest plan to adopt on a small scale with 

 suspicious water. After boiling and before drinking it should 

 be well aerated, as boiling, by driving off CO „ and air, renders 

 the water insipid and indigestible. 



(3.) Alum is often employed to purify water from suspicious 

 matters, 



(4.) Addition of limewater lessens the hardness of water as 

 already mentioned, and rapidly throws down the suspended 

 matters, as well as bacterial organisms, which become entangled 

 in the sediment. 



(5.) Sodium carbonate with boiling throws down lime and 

 possibly lead if present. 



(6.) Addition of potassium or sodium permanganate removes 

 the smell of hydrogen sulphide, and also carries down suspended 

 organic matter. 



(7.) Perchloride of Iron is a powerful oxidizing agent, and 

 throws down finely suspended organic matters. 



(8.) Spathose and spongy iron are powerful filtering 

 materials. 



Tests for the Purity of Water. 



It is often a matter of extreme difficulty to state positively 

 from either chemical or bacteriological examination of water, 

 whether it is free from organic impurity, or pathogenic micro- 

 organisms. Either test applied alone is insufficient, and the 

 application of both does not always solve the question. Valuable 

 evidence on this point was given before the Koyal Commission 

 on Metropolitan Water Supply recently, by Sir G. Buchanan, 

 M.D., F.R.S., late Chief Medical Officer to the Local Govern- 

 ment Board, to the effect that neither chemical nor bacteriological 

 tests were to be relied on as to the purity of water ; that we did 

 notiknow how small an amount of morbific material, if it gained 

 access to the water, might set up disease ; and that the way to 

 gain information as to purity and safety was, to search out the 

 conditions surrounding watercourses and water services. 



