450 



THE CIVIL I']Ng:ini:i]r and archhect'S journal. 



[Dkckmbf.r, 



city of flic i'iir;iiK', we h:\\c the number uf reviiUitions of tlie wlieel, 

 and eoi)sei|neMtly tlie number of times file cylinders are tilled witli 

 sic.iin in an hour; and as we als(j Know tlie elastic force of lliis steam, 

 we can deduce from it the correspondiiif; cjnanlily of water. Com- 

 ])ariiij;- then this quantity of water which is etl'ective with the total 

 ([nantity expended by the boiler, we find the quantity which has passed 

 over with the steam in the liquid f(nin. In this calculation we take 

 account of the quantity of steam recjuircd to till the waste space at 

 each end of the cylinder, called the cUarann, and also of the reduc- 

 tion of vaporization caused by the slowness of the motion in ascending- 

 inclined planes, and of the loss by the safety valves. For this purpose 

 we make use of the results furnished by special experiments, whence 

 we deduce that, by reason of the action of the blast pipe, the vapori- 

 zation of locomotives varies as the fourth rout of tlieir velocity, and 



that the loss through the safety valves in ascending planes amounts 

 on an average to *l"l- of the total vaporization. 



The results of our experiments are contained in the following table. 

 It should be remarked that if, in auy one of these experiments we have 

 erred in adiniltiug the jiressure in the cyliniler to have been the same 

 as in the boiler, it will follow that the quantity of water which passed 

 over in the liquid state with the steam in that experiment was more 

 considerable than our determination makes it. We are therefore sure 

 that our results are not exaggerated. 



It should also be remarkeil tliat the loss liere observed cannot be 

 attributed to a ])artial condensation of the steam in the steam pipes 

 and cylinders, since these are placed in the boiler itself and in the 

 smoke-box, where they are constantly in contact with the flame, which 

 renders this supposition inadmissible. 



TABLE. 

 Experimculs ml the ijUiintiti/ <if ti-akr carried over icilh the si cam in I he liquid ntnlc inio Ihc cijimders of Incumolivex. 



From these expei-iments we learn that the quantity of water in the 

 liquid state carried over with the steam into the cylinders of locomo- 

 tives amounts on an average to I vi'J of the total vaiiurization of the 

 boiler, reckoned after deducting the loss through the safety valves. 



This determination suits the mean of the engines we submitted to 

 experiment, but we shall observe that the quantity of water which 

 passes over without being vaporized must necessarily vary in ditterent 

 engines, since it depends en the ]iarlicular construction of the boiler, 

 anci especially on the capacity of the steam chest. If this is very 

 small, no more, for example, than )l) times the capacity of the cylin- 

 der, a tenth part of the steam already formed will pass into the cylin- 

 der at each stroke of the jiislon, and thus the density of the remaining 

 stcain will be suddenly reduced to nine-tenths of what it was pre- 

 viously. This great change of density will immediately draw from 

 the liquid .i new' quantity of sleam to supply the (h'Hciency ; but it is 

 evident that this new quantity of steam will be evolved from the licpiid 

 with so much the greater violence, and will consequently carry with 

 it so much the more of the li(|uid, ;'s the medium into which it is pre- 

 cipitated is more rarefied. 11 then the steam chest were made to con- 

 tain lUU cylinders full, instead of KS as the difterence of density pro- 

 duced at each stroke would be only 0-Jl, the quantity of water carried 

 over w ith the steam would be so much less. Also, if the end of the 

 steam pipe is very little elevated above the level of the water in the 

 boiler, or if it is very large, the water will he more easily carried as 

 far as the entrance of the ))ine, and w ill be admitted into it in greater 

 abundance. 



The quantity of water carried along with the sleam must therefore 

 vary according to the construction of the boilers. But it is also in- 

 fluenced by circumstances independent of it, such as the intensity of 

 the tire and the dirtiness of the water: the inti-nsity of the lire, be- 

 cause it produces in the boiler a more or less violent current of steam 

 in the boiler for the (piaiitity of water which it contains, and the dirti- 

 ness of the water, in consequence of the scum which it forms on the 

 surface. 



The carrying over of water with the steam is produced, as we see, 

 without Ihe appearance of any external sign, because the water mixed 

 with the steam is dissipated in the air with it. Unt there are mo- 

 juentfi when this eft'ect is so violent, that it manifests itself externally 



in the form of an abundant fall of rain from the top of the funnel. 

 The engine is then said to prime ; and this takes place especially when 

 tlie boiler is too full, because then the steam chest is by so much re- 

 duced in ca|)acity, and the level of the water at the same time ap- 

 proaches nearer to the entrance of the steam pipe. 



The extent of the loss which was the subject of the preceding ex- 

 periments, explains how it is that some boilers expend water so rajiiilly 

 that it is impossible to keep them full, even at a very moderate speed, 

 and how it sometimes happens that, by merely changing the steam 

 dome, a reduction of near'y i5 per cent, of the expense of fuel has 

 been produced. 



(We regret to find that we cannot put much confidence in the re- 

 sults of the preceding ex|)eriments for several reasons : in the Hrst 

 place, M. de rainbour aiqiears to have made no allowance for leakages 

 arising from defects in the pipes anil joints, so common in locomotive 

 boilers; secondly, it seems highly prob.ible that the loss through the 

 safetv valves was very dirt'ercnt in the various e, glues submitted to 

 experiment, inv\hich case a considerable error might be committed 

 by eslimating it in all the experiments at O-l'J of the total amount of 

 steam generated. In the same manner the mean, U-G'-i, of the results 

 in the table can have no value whatever, being the average of ratios 

 varying from U-15 to C-iU ; which shows that the difterence of cir- 

 cumstances in the various experiments was such as to occasion an 

 essential dilVerence in the resu'ts. — Edi!ur C. E. and ,1. Joiinial.) 



Effe'ls nf Liulilniiii; nil Sliiji\s Miisl!:. — M. Scllicr has rcporlt"! to iIil' Aca- 

 di-my t)f Sc; cncrs in ta\iiur of Captain Arrowtniiili's jilan, as snitcrior lo llie 

 ap|il'calion of cmiduclors. Captain Arrowsmiih's sjsti'in is lo paint ihe 

 masis, vanis, anij trucks of the top niasls and Hagstalls \vi:h black, and on 

 the approach of a stonu to strike ilie small \\hi c fails. M. Arago dissented 

 Irum ihcse conclusions. ■• ■ 



Aiititiii'.l'i's. — In tligi^mt; under the foundation of an old liuiisc in Calherine- 

 street. l-',M'lcr. last Keek. I«el\e olil Hat loltU-s or llaf;ons. evidently of ihc 

 ['Ciiod ot the I5:h ccntiir) , several small vessels of earlhen\varc, a curiiais 

 cu[) or t'lnkard. and ihe re-i] of llie Court nay iamily were tliscoveLCil. This 

 seal is of verv larpc dimensions, hearing the arms oV ('oiirlcnay and Tall ot 

 eiuiilaznncd lo^ethcr. anil the IvCgend. June Ciini-teiinij Cnmi'tinstr linrniiite 

 Si;;illiii:i. the Lulv wlio uwneil it Ijeing the wife of the 4th Karl of Devon, and 

 died al.ont \iW.— Bristol .Macurij. 



