554 TROPICAL HYGIENE, SANITATION, ETC. 



(4) Fluorescence or resorcin thallin is traced by its colour, one in 

 one hundred million parts of water. Six ounces of the sub- 

 stance should be dissolved and distributed on the refuse 

 suspected of carrying the contamination. This will show 

 itself in the drains, wells, &c., in a short time if such con- 

 taminated water drains into them. Should the water happen 

 to be acid there will be no colour, but one must add some 

 caustic potash when making the solution. Pour plenty of 

 water on the refuse heap after the fluorescence has been dis- 

 tributed. Bromine will remove the colour when the test is 

 finished. 



One must always exclude the presence of the testing salts in the 

 water before making the test. 



WATER— PURIFICATION. 



The purification of all tropical waters is essential. 



For small c{uantities the apparatus must be small and the process 

 simple, rapid and efficacious. 



For large quantities there will be a permanent apparatus and the 

 process will be elaborate, slow and also efficacious. 



The ways and means will be also controlled by the peculiar con- 

 tamination to be removed as alg^e, lead, iron, &c. 



There are many methods, selected according to each particular 

 case, two or more of which may be used for the same water. 



For the personal use of travellers the best means are : — 



(i) Boiling. 



(2) Berkefeld's pump or ordinary filter. 



(3) Chemical soloids of calcium hvpochloride, &c., such as are 



supplied by B. W. and Co. 



Such methods can also be used for larger quantities. 



The principal means in general for water purification are 

 mechanical, chemical and filtering efTected by means of storage, 

 precipitation, chemicals, heat, electricity, filtration and oxidation. 



(1) Storage. 



This does not sterilize water. 



In water stored for one week, 99 per cent, of cholera organisms 

 will be killed. In that stored for three weeks none remained. 



In water stored for five to eight weeks the typhoid bacillus will 

 die, hence storage is a great help towards sterilization. 



Storage for one month with a series of reservoirs and a continuous 

 flow to avoid the development of algas, is said to be almost an absolute 

 protection against epidemic infections. Not only are the bacteria 

 enormouslv reduced but other unpalatable conditions and injurious 



