REMARKS ON THERMOMETRIC REGISTERS. 



29 



when brouglit into contact witli red hot iron for any length of 

 time becomes decomposed, it deposits either a portion, or even 

 the whole of its carbon, and becomes converted, in the former 

 case, into marsh gas, in the latter into hydrogen, both of which 

 give out but little light when burning. From these consider- 

 ations it becomes apparent that chy coal should be used, that it 

 should be heated as rapidly as possible, and the process not 

 continued beyond five hours. 



The retoits have been the subject of great improvements as 

 regards their shape, nature and arrangement. The old cylindri- 

 cal iron retorts have given place to flat-bottomed or even kidney- 

 shaped ones, clay vessels have been introduced to save the 

 destruction of the iron, and an arrangement which seems to be 

 perhaps the best is a combination of both plans. Seven clay 

 retorts are heated by a fii-e placed in the centre of them, the 

 flames play round these vessels and descending heat five iron 

 j-etorts. It is found that the metal is thus much less acted upon 

 than according to the old plan. According to Lowe's patent 

 one-half of the retort only is charged at one time, and openings . 

 ai-e made at each end; the halves are charged alternately. The 

 propriety of this arrangement seams doubtful, owing to the ready 

 decomposition of olefiant gas when in contact with a strongly 

 heated surface as already mentioned. According to Croll's 

 patent one half of the retort is charged with coal, the other half 

 with coke, when the coke becomes red hot, steam is driven in 

 (15 lbs. of water to 1 ton of Newcastle coal) which passing over 

 the re:l hot coke and becoming decomposed mixes with the gas 

 arisiu;r from the coal. The rationale of this process wiU be 

 mentioned hereaftei'. 



The pui'ification of the gas is perhaps the most important 

 part of the process, and is even, at the pi-esent day, constantly 

 liudergoing some improvement. The gas as evolved from the 

 retorts contains, among others, tlie following gases: — Olefiant 

 ^■is, lii;'ht cai'buretted hydrogen (marsh gas,) carbonic oxide and 

 liyli'i'g"-"- I'lie three latter are, in point of illuminating power, 

 nearly useli^ss, although they may perhaps serve as a diluent for 

 the otherwise too powerful olefiant gas ; their removal, therefore, 

 from the mixture would probably not be advisable, even if it 

 were possible. 



There are other substances, however, in the mixture, which if 

 allowed to remain would be positively injurious, such as carbonic 

 sulphurous and muriatic acids, sulphocyanogen, sulphuretted 

 hydrogen and ammonia ; of these, the fii-st five may be perfectly 

 removed by means of the hme purifiere, whether they be in a 

 free state or combined with ammonia, but this latter substance 

 itself will stiO remain, and has to be removed by some other 

 contrivance. As the simplest, and perhaps most economical, 

 may be mentioned the use of sulphuric acid, (Croll's patent) 

 the gas either before or aft«r its entrance into the lime purifiers, 

 is passed through dilute sulphuric acid, the ammonia remains 

 behind in combination with the acid, forming a salt (sulphate of 

 ammonia) which is exceedingly valuable as a manure, and has 

 lately been strongly recommended for many horticultural pur- 

 ])ose?. The quantity of salt thus obtained is not inconsiderable, 

 inasmuch as the gas contains about j^th of ammonia. The gas 

 is stated to be very much improved by the separation of ammonia 

 in several respects; firstly, its illuminating power is increased 5 

 per e«ut; and secondly, its corrosive action on brass or copper, 

 jets and pipes is materially diminished. Moreover, by the pre- 

 vious removal of the ammonia, the lime used in the purifiers 

 does not acquire so disagreeable a smell as when not thus treated. 

 Besides the foregoing patented process of Croll, there are numer- 

 ous othei-s for the removal of ammonia from coal gas, all depend- 

 ing upon bringing it into contact with some substance which 

 may either combine directly with it, or else by a decomposition 

 may effect its removal. For instance, bone dust dissolved in oil 



of vitriol is sometimes iLsed, yielding a most valuable manure. 

 Various acids, and even neutral salts, (for instance, the common 

 green vitriol, or sulphate of iron) are recommended in Johnson's 

 patent. Philippi and Mallet recommended salts of manganese, 

 which can he obtained in large quantities from the residues in 

 bleaching works. Croll uses sulphurous acid as a purifier, by 

 which rather large quantities of sulphur are obtained ; but in 

 aU these processes it is still necessary to employ either a wet or a 

 diy lime purifier before the gas is rendered fit for use. The 

 residue from the hme vats has a most detestable smell, and is 

 scarcely to be recommended for agricultural piu-poses until it has 

 either been roasted, or exposed for a length of time to the 

 atmosphere. 



An exceedingly curious and ingenious process has been pa- 

 tented by Mr. Laming by which the pm-ification of the gas is 

 effected by the chemical action of its own impurities on materials 

 which do not require to be renewed at such short periods as is the 

 case with lime. A solution of the chloride of iron is mixed with 

 either lime or chalk, sawdust is then added, and thus a porous mass 

 is prepared in which after exposure to the air, the principal and 

 active ingredients are lime, peroxide of iron, and muriate of lime. 

 The sidphuretted hydrogen is absorbed by the oxide of iroii and 

 sulphuret of iron formed, carbonate of lime is also produced, and 

 according to Mr. Laming muriate of ammonia likewise, although 

 the chemical process which effects this formation does not seem 

 to be very clearly made out in his description. 



The mixture absorbs the impurities very perfectly, and possesses 

 this advantage, that on being exposed to the atmosphere it has 

 no disagreeable smell, but becomes rapidly oxidized, the sulph- 

 uret of iron passing into sulphate, which salt is again decomposed 

 by the chalk, (carbonate of lime) and thus the mixtm'e of itself 

 returns to its original condition, viz., peroxide of iron and chalk. 

 After being used a number of times the salt of ammonia accum- 

 ulates to such an extent as to impede its action, in that case it 

 only needs to be washed well, in order to restore to the mixture 

 its original efficacy. 



(To he Continued.) 



Remarks on Thermometric Registers; by Capt. J. H. 

 Lefroy, R. A., F. R. S. 



One of the firet physical enquiries to which the attention of 

 the occupants of a new country is naturally directed, seems to be, 

 m almost eveiy case, the Temperature of the Air; and this 

 choice is justified, not only by the intimate personal concern we 

 all have in that question, but also by the circumstance that the 

 greater part of the other phenomena of the weather, that is, of 

 meteorology in relation to the business of life, depend more or 

 less immediately upon it. And there is a particular interest in 

 all such observations as date from that gTeat epoch in the physi- 

 cal history of a country, in which it first becomes the abode of 

 civilized man. It then begins to imdergo those superficial changes 

 which his industry toils to effect. From such observations must 

 be taken, at a futui'e period, the data for a number of refined 

 enquii'ies of the greatest intei'cst. By reference to them we leam, 

 or ought to leai-n, whether we can bring about changes of chmate 

 by human agency : whether such changes are always beneficial, 

 and therefoi-e in harmony with the design of the Universe : or 

 sometimes noxious, and therefore in favour of the opinion that 

 there are pre-ordained bounds to the extension of cinlized man 

 over the Globe : if we may credit Father Hue, the first result of 

 the extension of Chinese industiy into Independent Tai-taiy, has 

 been to render the countiy uninhabitable: may no such result 

 follow the invasion of Canadian woods by British ploughs, but 

 thus we learn that such a thing is within the bounds of possibil- 

 ity. Again, inseparably connected with the settlement of a 

 country, is the gradual disappearance of w'hole classes of the 



