244 



NATURE 



[7;//r 25,1872 



or mention of a Bishop Mamcrtiis, or of some intrusive 

 bishop who may have been Mamertiis ? Labbe's " Sacro- 

 sancla Concilia" (at the British Museum or the London 

 Libraiy) might be consulted to see whether any hint is 

 t;ivcn of Mamertus having been in Italy, either in tlie 

 letters of Leo, or (more probably) in those of his successor, 

 Hilary (iv. pp. 1032 — 1047). 



Procopius got his information during the first Gothic 

 war (A.D. 535 — 540) ; the second lasted from A.D. 544 to 

 A.u. 548. He died about A.D. 565, at the age of 60. 

 Ought the " centuiy or more ago "to be computed from 

 the date of his inf'ormation, or from the time when he 

 wrote ? This might make a difference of 10 or 20 years. 

 If the former, then the commencement (?) and violence 

 of the eruptions are thiown back to the early part of the 

 fifth centui7. In any case they must have preceded rather 

 than followed the interval from 455 to 463, Where did 

 Prof. Daubeny get his date of A.D. 472 .' Certainly not 

 here. 



It is theiefoic very likely that about A.D. 455 Vesuvius 

 may have been in a state of violent activity. In that year 

 Rome was sacked. These are precisely the conditions 

 which the hypothesis requires. Procopius was told that 

 the Rogations were occasioned by such eruptions at about 

 that date. If, then, Mamertus was the sole (?) author of 

 them, he must have been present where the Terrors oc- 

 curred. Is there positive e\idence of the fact? If no 

 positive evidence, for or against, can be found, it will then 

 be time enough to go into other questions of probability. 

 Here for the present I conclude. 



Henrv Norton 



; VA TER ANAL\ 'SIS 



n. 



IN the last article* we assumed that the object of 

 estimating the organic carbon and nitrogen has been 

 fully understood by the reader ; but in order to render 

 all chance of our meaning being misunderstood in the 

 remarks which arc to follow, it vill be as well to briefly 

 capitulate the reasons which lender these determinations 

 so valuable. Carbon and nitrogen fotm with hydrogen 

 the principal constituents of all organised bodies, and 

 hence are found in all the excreta of animals. Nitro- 

 gen is found in animals to a much greater extent than in 

 plants, while in the inorganic world this latter element is 

 scarcely found at all, and carbon only in the form of car- 

 bon, coal or carbonic acid, none of which bodies are likely 

 to be found in water except the last, the first two being 

 insoluble. It hence follows that if a large quantity, or 

 indeed any quantity, of carbon and nitrogen be found in 

 water, their source can only have been organic in its 

 nature, and if the proportion of nitrogen to carbon be 

 more than one to five, the source is almost absolutely 

 certain to have been animal. 



Accordingly, when we find these two elements exist- 

 ing in waters in the proportions just indicated, we are 

 justified in assuming the presence cf some form of 

 animal or organic contamination in them ; and of 

 all forms in which this contamination can e.\ist, sew- 

 age is the most probable. It will thus be seen that 

 when chemists assert that a water is contaminated with 

 sewage, they do so on grounds the truth of which is easily 

 demonstrable. That such waters containing effete ani- 

 mal matters are injurious, no arguments of ours will be 

 required to prove ; no persons of authority in sanitary 

 matters have presumed to assert that such waters are 

 harrniess. 



With regard to the method of obtaining evidence as 

 to this contamination, however, considerable difference of 

 opinion exists, and in the former paper we have endea- 

 voured to show the worthlcssness of the early processes 

 of estimating organic matter by ignition of the residue. 



and by treatment with permanganate of potash ; and 

 though this last process is condemned by all, it is still 

 in use. 



We have also given reasons for regar'ding with dis- 

 trust the results obtained by the use of Chapman, 

 Wanklyn, and Smith's method of indirect determination 

 of organic matter from the amount of ammonia evolved 

 by the water, as we maintain that it cannot be shown that 

 the ammonia evolved bears any distinct relation to the 

 amount of organic matter present, and that with many 

 waters it is difficult to obtain an accurate estimate of the 

 ammonia thus evolved. 



The process we have now to consider bases its claims to 

 confidence on the fact that it gives an absolute determina- 

 tion of the quantity of carbon and nitrogen present in the 

 water, and that it does do this can, we think, be proved 

 without much difficulty. 



The process is based upon the fact that when a body 

 containing carbon and nitrogen is heated in contact with 

 cupric oxide to bright redness, the carbon is conver'ted 

 into carbonic anhydride at the expense of a portion of the 

 oxygen of the cupric oxide, while the nitrogen is liberated, 

 partly in the free state and partly in the forms of its lower 

 oxides, the quantity cf these latter being reduced as much 

 as possible by causing them to pass over the surface of 

 red-hot metallic copper, which abstracts the oxygen and 

 leaves the nitrogen free. In other words, the substances 

 are obtained and estimated by what is known to chemists 

 as a " combustion." 



As far back as 1864 an unsuccessful attempt had been 

 made by Wellzien to apply this process to the estimation 

 of carbon in water. The failure was due to the very 

 minute quantities available for estimation, and to the fact 

 that the water was rendered acid with sulphuric acid 

 before evaporation, a proceeding which dir'ectly tended 

 to. vitiate the results, even had no other obstacle inter- 

 vened, as the acid gradually concentrated during evapo- 

 ration, ultimately became sufficiently strong to char and 

 decompose much cf the organic matter present. 



It was not until Dr. Hermann Sprengel had placed in 

 the hands of chemists a new and powerful means of re- 

 search in the shape of the admirable air-pump which 

 bears his name, that it was possible to estimate directly 

 the minute amounts of carbon and nitrogen which water, 

 as a rule, contains. 



In March 1868 Messrs. Fr-ankland and Armstrong pub- 

 lished a method of water analysis which they had elabo- 

 rated, after eighteen months' work at the subject. 



A quantity of water proportionate to the amount of am- 

 monia found,* and varying from one litre in the case of a 

 town water-supply, to 100 cubic centimetres in the case of 

 a much polluted water, is introduced into a flask, and 1 5 

 cubic centimetres of a saturated solution of sulphurous 

 anhydride arc added, and the water boiled briskly for 

 three minutes ; the water is then removed from the source 

 of heat, and a portion introduced into a hemispherical 

 lipless glassdishof about 100 to I20cubiccentimetres capa- 

 city ; this is placed on a steam bath, and to the first dish- 

 ful two or three drops of a moderately strong solution of 

 ferric chloride are added. Should the water leave but a 

 small solid residue, or contain little calcic carbonate, a few 

 drops of a solution of sodic sulphite should also be added. 

 The dish is then covered with a cap of filtering paper 

 stretched over a ring of cane, and the evaporation con- 

 tinued, the rest of the water being kept warm in the flask, 

 and added from time to time to the dish. The laboratory 

 in wliich this operation is performed should be kept free 

 from dust, and no ammonia should ever be allowed in it. 



The rationale of the process so far is very simple, and 

 is as follows ; — The first boiling with sulphurous acid ex- 

 pels the free carbonic acid in the water, and also any that 



• If ihc .-inimonia be less than o'l part per loo.coo, i litre sliouMlie u-cil ; 

 if more than i o, a luintlretl cubic ccntimcues or less. (Sec Siitlniis 

 " Volumetric An.-ilysis." J. A. Cliurchill, New Ilurliiiglon Slrtcl, ii.il 

 Eililion, 1871, PI> ;.|6-=95.) 



