1869.] The Future Water-supi)hj of London. 237 



London Water Bills,* he stated that in the London Hospital, 

 which is exclusively supplied with water from Old Ford, there was 

 not, dming the whole of the epidemic, one case of cholera ^mong 

 the ordinary inmates or attendants of the hospital. This statement, 

 which is said to have been repeated before the Eoyal Commission 

 on Water-supply, would, if correct, have supplied us with a still 

 more curious instance than that of the Limehouse schools; but, 

 unfortunately, it appears that Ur. Letheby's knowledge of his 

 own hospital was inaccurate, for in the official hospital returns 

 Mr. Bathurst Dove gives a detailed account of seven cases of cholera 

 which occurred among the hospital attendants, and one among the 

 ordinary patients. Six of these cases terminated fatally, including 

 the patient, a child ; so that, out of the 130 attendants employed in 

 the hospital, five died — a proportion of 385 in 10,000 ! 



It is now necessary to consider the amount and nature of the 

 evidence which science is able to offer on the quality of water 

 intended for drinking purposes. With respect to the mineral con- 

 stituents of a sample of water, chemical analysis, of course, enables 

 us to speak with great certainty and accuracy ; and geology can, in 

 most cases, account satisfactorily for the results of the analysis. It 

 seldom happens, however, that a water which is used for drinking 

 purposes contains any ingredient which, either from its nature or 

 exorbitant amount, is likely to be deleterious to health. When 

 calciiun or magnesium salts are present in large quantity, they 

 render the water inconveniently hard, and are therefore objec- 

 tionable, as leading to an enormous waste of soap; but this is a 

 subject which has been so fully discussed by Dr. Frankland in this 

 Journal that it may now be passed over. Some of the mineral con- 

 stituents which are found in ordinary waters, though entirely 

 harmless in themselves, are yet of great significance, as throwing 

 light on the previous history of the water. Thus ammonia and 

 nitrous and nitric acids must be determined with the utmost care m 

 the examination of a water, because, with the exception of a small 

 and never-exceeded quantity which is derived from rain, they arise 

 in the great majority of cases from the alteration of animal exuvias 

 in the water. So, again, with common salt and other chlorides. 

 Though sometimes present naturally in waters uncontaminated with 

 organic matter, any large quantity of them may generally be regarded 

 as a sign that sewage contamination is present. For an analogous 

 reason the gases dissolved in water yield valuable indications ; oxygen 

 being usually deficient and carbonic acid in excess when organic 

 matter has undergone recent oxidation in the water. All these 

 constituents can be estimated with the most astonishing accuracy 

 even when present in extremely minute quantity, and it is from a 



* ' Minutes of Evidence,' p. 45. 



