Mabch 1, 1894.] 



KNOWLEDGE 



57 



weigh the residue, from which result the amount per 

 gallon is calculated. The amount of solid residue left on 

 thus evaporating some of the Zem-Zem water corre- 

 sponded to two hundred and nineteen grains per gallon — 

 a quantity characteristic of a strongly saline water. 



Since chlorine (in combination with sodium as common 

 salt) is one of the substances given off from the skin, its 

 presence in water in any large quantity is an indication of 

 probable sewage contamination. Should a water be found 

 to contain as much as nine grains of chlorine per gallon, 

 it would be looked upon with strong suspicion, although, 

 if the well or spring from which it was taken should 

 happen to be situated near a salt bed, the chlorine 

 might be derived from that source. The amount found in 

 the Zem-Zem water, viz., sixty-nine grains per gallon, 

 whether derived from the soil or, as is highly probable, 

 from the skins of the Arab pilgrims, condemned it 

 absolutely. 



The hardness was determined by a method devised by 

 the late Dr. Clarke, and known as " Clarke's soap test." 

 It consists in adding a solution of pure soap, of which the 

 strength is known, to the water, until a permanent lather 

 is produced. Each successive portion of soap solution 

 added corresponds to a definite quantity of carbonate of 

 lime, or its equivalent of other salts, dissolved in the 

 water. As no lather can be produced until the soap has 

 neutralized the whole of the lime or magnesia in the 

 water, we can estimate very rapidly the hardness hi this 

 way. This is usually expressed in degrees, each of which 

 corresponds to one grain of carbonate of lime per gallon. 

 Thus, to say a water has fifteen degrees of hardness means 

 that it contains constituents which produce the same 

 degree of hardness that fifteen grains of carbonate of lime 

 per gallon would do. The Zem-Zem water had forty- 

 three degrees of hardness — about three times that of an 

 average water. 



The quantity of albuminoid ammonia is one of the most 

 important data in estimating a water. A good water should 

 not contain as much as -1 part of ammonia in a million 

 of water. The quantity of albuminoid ammonia in the 

 Zem-Zem water, viz., 2-2 parts in a million, was character- 

 istic of sewage effluent, and confirmed the conclusion 

 already arrived at from the estimation of the chlorine. 



Prof. Crookshank was kind enough to make an exhaus- 

 tive bacteriological examination of some of the water, but 

 was unable to find any trace of living organisms. The 

 water was sterile, as might well be expected after its 

 having been hermetically sealed and in total darkness 

 during forty years. 



The folio wmg were the quantities of some of the principal 

 constituents of the water : — • 



SEWER GAS AND ZYMOTIC DISEASE. 



By A. C. Kanyard. 



THE fear, amounting to terror, lest we should breathe 

 a whiff of sewer gas, has had potent and far- 

 reaching intluences on modern life. What is 

 known as Sanitation has increased by leaps and 

 bounds during the last quarter of a century, until 

 the dread of sewer air has become a factor in legislation 

 sufficiently powerful to procure the passing of Acts of 



Parliament that materially modify the rights of English- 

 men ; and yet most of the theories of the so-called Sanitary 

 Science have been arrived at by the deductive method, 

 which seriously led astray the pioneers of thought when 

 groping after the first discovered laws of the physical 

 sciences. 



Perhaps the theory which has been most fruitful in 

 causing a lavish expenditure on sanitary appliances (the 

 fashions of which change almost as rapidly as the fashions 

 in feminine head-gear) is the theory that sewer gas is 

 heavily charged with the germs of disease. It is founded 

 on two assumptions, both of which have been received as 

 self-evident. The first assumption is that sewage matter 

 swarms with the germs of disease ; and the second is that 

 the micro-organisms living in sewage matter can rise into 

 the air with the effluvia or smell from sewage, and are 

 carried wherever the sewage smell can be detected. To 

 the more thoughtful there seemed to be a difficulty in 

 supposing that micro-organisms could be carried into the 

 air by evaporation. But the difficulty was quickly met by 

 the theorists, who suggested that bubbles of gas must 

 rise from the sewage sludge, and that such bubbles on 

 bursting would project minute globules of liquid into the 

 air, and the minute globules might carry the dangerous 

 micro-organisms. The tlieory was ingenious, it was easily 

 understood and was widely adopted, and the logical and 

 natural consequences of panic and legislation followed. 

 The public is not so deficient in the power of making 

 logical deductions as it is deficient in the critical faculty 

 which should lead us to test by experiment the axioms 

 we too readily accept as self-evident. 



It was not till 1883 that experiments were made by 

 M. Miguel in the Paris sewers to determine the number of 

 micro-organisms per litre of sewer air as compared with 

 the number of similar organisms in the air above ground. 

 He found an average of from 0-8 to 0-9 per litre in the air 

 of the sewer under the Rue de Rivoli, in the neighbourhood 

 of the point where the sewer joins the large collector of the 

 Boulevard Sobastopol; and he states that the organisms 

 in the air of the Rue de Rivoli may in summer exceed in 

 number the organisms in the sewer air by five or six times, 

 whereas in winter the ratio may be reversed. 



Then followed a series of investigations on the subject, 

 undertaken by Drs. Caruelly and Haldane, who made 

 observations in the main sewer of Westminster Palace and 

 in various sewers in Dundee. The general results they 

 arrived at were that — 



1. The carbonic acid gas in sewer air is about twice as 

 much, and the organic matter about three times as much, 

 as in the outside air at the same time. 



2. The number of micro-organisms is less in sewer air 

 than in the outside air at the same time. 



3. The quantity of carbonic acid, organic matter, and 

 micro-organisms in sewer air is less than in the air of 

 naturally ventilated schools, and, with the exception of 

 organic matter, it is less than in the air of mechanically 

 ventilated schools. 



i. Sewer air contained a much smaller number of 

 micro-organisms than the air in any class of house they 

 had investigated. 



During the last year and a half, Mr. J. Parry Laws has 

 been occupied on a series of experiments made on behalf 

 of the London County Council in the sewers of the 

 Metropolis. The first sewer experimented upon was that 

 known as the King's Scholars Pond sewer, which runs in 

 a straight line under the Green Park from Piccadilly on 

 the north to the Buckingham Palace Road on the south. 

 It was constnicted some one hundred and twenty years 

 ago, and has therefore been in use long enough, as 



