Jan. 2, 1885.] 



♦ KNOWLEDGE ♦ 



©tlensive when fresh, but remains so after keeping for two 

 or three months, or longer.'.' 



" The process which goes on in the mixture is obviously 

 one of disintegration, ami of some combination between the 

 eiirth and the organic matter, as is evidenced by the disap- 

 poArance of stools and even of paper among the other con- 

 stituents of the con^po^t But the absence of fu-tor from 

 the mixture of earth with stool or urine, even with pro- 

 longed keeping, shows that decomposition in the ordinary 

 sense does not take place." lie then goes on to state that 

 the various forms of earthclosets, used cither within or out 

 of the house, which have come under his careful ob.serva- 

 tion, have always been found to be quite wholesome. This 

 may be taken as ample testimony to the ellective working 

 of the system iu the isolated dwelling-house. 



As a second instance, we may consider its value when 

 applied to large institutions and temporary gatherings of 

 prolonged duration. In quoting from the reports of Dr. 

 l>uchanan, we may here make use of two special examples, 

 which will serve to point out advantages ot cardinal virtue 

 in the exhibition of the system. In commenting upon the 

 Dorset county school at Dorchester, where provision has 

 gradually been made since 18G."), he says: — "When the 

 school was furnished with water-closets, the cost for 

 ft'pairs of them used to exceed £.3 a-year. In the four 

 years since the adoption of earth-closets, the entire charge 

 for repairs has been less than 10s. Under the water-closet 

 system there were frequently offensive smells, and diarrho-a 

 was occasionally epidemic. Since the introduction of the 

 earth system, there have been neitlier offensive smells nor 

 diarrhiea. In 18GG and 1867 there was a good deal of 

 ' low fever ' in the parts of Dorchester round the school, 

 but there was none in the school itself." Again, with 

 regard to the Broadmoor Criminal Lunatic Asylum, he 

 observes: — "Upon my visit on Dec. '29, 18G9, several 

 urinals were found to have their water-supply frozen up, 

 and smell was coming from them. But the earth-closets 

 were in most instances quite free from smell, although 

 where they had been misused by slops thrown into them 

 (iu a part of the establishment where their use was most 

 recent and least understood) there was some smell from 

 them. 



"P.S. — March, 1870. The closets in this and other parts 

 of the asylum are now found in perfect order, witliout the 

 least smell from any one of them. The ojiportunity of the 

 frost, however, enabled comparison to be made with what 

 must necessarily have been the condition of water-closets 

 under similar conditions of use. The earth-closets, when 

 properly used, were clean and odourless ; water-closets 

 without water, used by more than ten persons each, must, 

 however carefully used, have been foul and offensive. 

 Moreover, the Superintendent informed me that .£70 had 

 been paid for repairs to the water-closet pipes after a hard 

 frost some few years ago, whereas under the earth system 



frost can do no mischief A saving of water, 



estimated by Dr. Meyer to amount to nearly half the 

 quantity previously used, and involving a corresponding 

 economy ui coals and pumping, is also to be considered in 

 relation to questions of cost. Such economy of water was, 

 indeed, one of the reasons for the substitution of the earth 

 for the water system." 



In our next communication we shall consider the value 

 of the process in relation to other types, such as its appli- 

 cation and results in relation to villages and towns, with 

 specially interesting example?, and a concluding summary. 



Ebeat.1.— On p. 499, col. 2, line 9 of the article on " A Marvellons 

 Little Stream," the word " atmite " should be " auprite." On p. 500, 

 col. 2, lines 3 and 4, the dash ' should be transposed from the second 

 E to the first. 



K I, VA'T !{()-? I.. \ 'V I NM{. 



Bv \V. Si.iNco. 



XVI.— IN Til 10 1!.\T1I .\M) OUT OV IT. 



rpiIE objects destined to receive a coating of silver 

 X having been duly suspended from the cathode (the 

 rod in connection with the zinc |>ole of the battery) and 

 immeised in the el.ctrolytic bath, and the battery circuit 

 having been completed, attention must be ccntn^d on the 

 bath and its behaviour. It is possible that, after every 

 conceivable precaution has been taken in the preparation to 

 ensure .success, failure will ultimately result, unless due 

 regard be paid to the ellicicncy with which the various parts 

 of the bath continue to perform their respective functions. 

 It is noteworthy that when a solution is first used, its 

 action is somewhat irregular, and may ))Ossibly lead one to 

 think that something is radically wrong. This trouble, which 

 is probably due to mechanical or iihysical inequaliti(>s, soon 

 disappears, and, if all is as it should be, the deposition of 

 the metal will proceed with brcoming regularity, and give 

 every satisfaction, for a time at least. In a previous article 

 it was intimated that a cpiantity of free cyanide of potas- 

 sium should be present in the solution for the purpose of 

 facilitating the conversion of the silver plat(i forming the 

 anode into the cyanide of silver. Now, the cyanide of 

 potassium is assailable by carbonic aciJ, which converts it 

 into the carbonate of potassium, while hydrocyanic acid is 

 set free. 



It is well-known that our atmosphere contains a propor- 

 tion, small though it be, of carbonic acid, and it is this acid 

 which acts dcleteriously upon the cyanide, converting it 

 into carbonate of potassium, in consequence of which the 

 solution has a tendency to become weak iu silver. In order 

 to maintain the solution in good working order, a little 

 additional cyanide of potassium should be poured in from 

 time to time. The necessity for this additional cyanide is 

 evidenced by the altered apiiearauce of the silver plate, 

 which, under favourable circumstances, has the charac- 

 teristic pure white tint, but when the free eyani'le has 

 become neutralised, it is converted to a dirty or dull grey 

 colour. The metal is less readily dissolved, and the action 

 of the bath becomes sluggish. 



Temperature, it will be evident on reflection, has a con- 

 siderable influence on the quality and rapidity of the 

 working, seeing what an immense part heat jilays in varying 

 the degrees of solubility for all kinds of substances in all 

 kinds of solvents. Experience shows that the temperature 

 at which the Viest action takes place is about G0° Fall. The 

 quality of the deposit is considerably improved and its 

 regularity largely increased by imparting motion to tli!? 

 object while it is in the cell. If constant motion cannot 

 be maintained, an intermittent one, even if only at 

 long intervals, should be imparted. If a solution 

 be kept peifectly still, having immersed in it a plate 

 of silver and a plate of, say, copper, connected to the 

 copper and zinc jjoles of the battery respectively, it will 

 be found that the upper part of the silver will be very ex- 

 tensively dissolved as compared with the lower part, while 

 the densest deposit occurs on the lower part of the copper. 

 This, at first sight, would appear to indicate that the 

 electrolytic action takes place diagonally. A little reflec- 

 tion will, however, make it apparent that this is not neces- 

 sarily the case, but will make it evident that the real cause 

 is involved in a i-imple question of specific gravity. The 

 cyanide contiguous with the silver dissolves it, and the 

 liquid being thus much heavier falls. At the surface of 

 the copper, silver is withdrawn, and the solution being pro- 

 portionately lighter rise,''. Copious depo-iits are, therefore, 



