DRINKING WATER FOR TRAVELLERS IN THE TROPICS 509 
were very hard. The latter did not dissolve readily, so that it became necessary 
to powder them by folding the tablet in paper and striking it with a knife-handle. 
The powder was then added to the water and mixed well by shaking. 
Dakin and Dunham! originated the use of halazone for the sterilization of 
drinking water, and they gave the substance this name. The chemical name 
of the active chlorinating substance is para-sulphonedichloramidobenzoic acid 
and the formula is CsH,(SO,NCl,)COOH-1: 4. The tablets recommended by 
Dakin and Dunham weighed 100 to 105 mg. and contained four per cent of the 
acid above mentioned, four per cent of sodium carbonate and ninety-two per 
cent, or slightly more, of sodium chloride. They found such tablets to be more 
stable than other similar compounds known to them. When kept in amber- 
colored bottles under ordinary conditions no decomposition was noted in two 
months. Such a tablet is manufactured by the Abbott Laboratories, of Chicago. 
The Monsanto Chemical Works, of St. Louis, also manufacture halazone, but I 
have had experience only with that of the Abbott Laboratories. 
Tests made by Dakin and Dunham indicate that the acid in the tablet above 
described, when used in a ‘‘concentration of 1: 300,000, is sufficient to sterilize 
an ordinarily heavily contaminated water in about thirty minutes.” They ob- 
served, further, that this concentration gives a taste of chlorine which is just per- 
ceptible. 
One tablet added to a quart (or liter) of water gives a concentration of the 
acid of about 1: 250,000 and, because the acid contains about twenty-five per 
cent of available chlorine, a proportion of chlorine of about 1: 1,000,000 is ob- 
tained if the tablet be of full strength. 
Because deterioration of halazone through exposure to air under tropical 
conditions had been feared, our halazone was packed in vials containing only 
twenty tablets each. These vials were well corked and sealed with paraffin. 
Eighteen months later, and after a year in tropical Africa, the corks of unused 
bottles were still in place and the sealing intact. 
That the moderate excess of tablets used by us to give a strong taste of 
chlorine in the Congo water was required by impurities in the water, and not by 
deterioration of the tablets, is indicated by the fact that subsequent analyses of 
tablets from two of our vials showed no evidence of appreciable deterioration 
(see Mr. Clark’s analysis below). 
Although strong solutions of chlorine may corrode metals, the low concentra- 
tions required for the sterilization of water are not likely to injure vessels such 
as galvanized iron buckets or aluminium canteens. Therefore, such metal 
containers may be used for water which is in process of chlorination or which 
has been chlorinated. 
Test ANALYSES 
The results of his chemical analyses were kindly reported on October 31, 1927, 
by Mr. H. W. Clark, of the Department of Public Health of the Commonwealth 
of Massachusetts. Mr. Clark says: ‘Both solid and disintegrated tablets were 
1 Brit. Med. Journ., Vol. 1, p. 682, May 26, 1917. 
