310 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL, 



LNovEilBKK, 



into exact contact at their ends, and cementing over them a brass 

 tubuhire, grooved to fit them outside. This brass tubuliire liad a 

 rectanf;iilar tube opening into it, into which was cemented a capil- 

 lary tube, by means of which connnunication was made with an 

 air-pump, so as to dry the apparatus and introduce the gases to be 

 operated on. 



The boiler contained oil, which was constantly agitated so as to 

 maintain an uniform temperature throughout the whole bath. 



The method of operating is as follows : — 



In the first place, to dry the apparatus, a little mercury is put 

 into the inner manometer tube, and the stop-cock so placed as to 

 cut off this tube from communication with the other and with 

 the opening. The lateral tube of the tubulure is then put into 

 communication with an air-pump furnished with several tubes 

 filled with pumice soaked in concentrated sulphuric acid, which 

 are intended to absorb the moisture. A vacuum is made a great 

 number of times, and each time the air is allowed to enter very 

 .slowly. To be sure that the drying is complete, the globes are 

 heated to SO' or 60° (122° to 140° Fahrenheit). The pump is then 

 removed, but the tubes are left open in communication with the 

 drying tubes. Suppose now that it is desired to compare the 

 movement of a thermometer containing air whose elastic force 

 at 0° is 76 mm., with that of another containing air of a less elastic 

 force. 



The two globes are surrounded with melting ice, and the stop- 

 cock of the first manometer being so placed as to make a commu- 

 nication between the two manometer tubes, mercury is poured in 

 so as to raise its level to a mark placed near the top of the inner 

 tube (that is, the one communicating with the reservoir). The 

 two mercurial columns will be necessarily at the same level, 

 because the apparatus communicates freely with the air by the 

 tubulure. 



On the other hand, a partial vacuum is made in the second globe, 

 and the rarefaction of the air in it is determined by the difference 

 of height of its manometric columns ; when a proper rarefaction 

 has been attained, the apparatus is closed by hermetically sealing 

 the lateral capillary tube of the tubulure, and mercury is then 

 poured into the manometer until its surface stands at a mark 

 made near the top of the inner manometer tube. 



The elastic forces are measured by four properly-placed catheto- 

 meters, each one being so placed as to be able to foUow the 

 meniscus in one of the tubes. 



The necessary observations of the height of the barometer, and 

 the position of the meniscus of each of the manometer tubes being 

 made, the lateral tube of the first reservoir is then hermetically 

 closed, the ice removed and replaced by oil which is heated by a 

 furnace ])laced under it. The oil bath is heated until the tem- 

 perature at which the two instruments are to be compared is at- 

 tained, the air-holes of the furnace are then more or less closed 

 and the oil kept in constant agitation ; and the thermometers are 

 adjusted for observation by pouring mercury into the manometer 

 tubes, so as to bring back the level of the columns in the inner 

 tubes to the marks made upon them. The temperature then rising 

 only very slowly, the movements of the four columns of mercury 

 are simultaneously watched, and when they are perfectly station- 

 ary, at a signal given by one of the observers the barometer is 

 read, and the temperatures of the air in the vicinity of the mano- 

 meter tubes, and of the lateral tubes attached to the reservoirs, 

 noted. 



As it is essential in this mode of experimenting to keep the 

 temperatures stationary as long as possible, they should be raised 

 very slowly when approaching the maximum at which the observa- 

 tions are to be made, and by a little practice a series of observa- 

 tions may be got at temperatures not differing more than 1° 

 from each other, and the observer be assured that one instrument 

 is not behind the other in its indications. This precaution is 

 above all indispensable when the air thermometer is compared with 

 the numerical. 



It is not necessary, and would be very difficult, to bring the 

 mercury in the manometers exactly to the marks. It is sufficient 

 to bring them nearly there, and as the observations give exactly 

 their differences of level, the volumes can easily be calculated 

 when the tubes have been gauged in the vicinity of the marks. 

 The experiments upon tliermometers filled with different gases 

 are conducted exactly in the same way. 



These globes were too thin to permit the experiments upon 

 thermometers filled with air at a much higher pressure than 

 76 mm. to be tried with them ; recourse was had to others similar, 

 but having their walls 3 or i mm. thick. These globes were of 

 rather less capacity than the former, holding only about 600 cubic 

 ceatimetres. 



A great numljer of experiments were made by M. Regnault 

 with the apparatus in which air of ordinary density was com])ared 

 with that of much less, and with that of much greater density, 

 as well as with hydrogen gas, carbonic and sulplmrous acid, and the 

 principal conclusions which lie draws from them are as follows ; — 



1. The atmospheric air follows the same law of dilatation from 

 0° to 350° (32° to 662° Fahrenheit) of temperature, even when its 

 initial elastic force at 0° varies from O-m* to l-n^S, (1-33 to 

 4'25 ft.). So that in the construction of an air thermometer, no 

 attention need be paid to the density of the air introduced, — the 

 instruments will be comparable whatever may be the density. 



2. Atmospheric air, hydrogen gas, and carbonic acid, follow 

 between 0° and 3.50', sensibly the same law of dilatation, although 

 their coefficients of dilatation are sensibly different. So that the 

 thermometers made with these different gases will accord, jirovided 

 the temperatures are calculated from their proper coefficients. 

 From this it follows that the coefficients of dilatation of these 

 gases present sensibly the same ratio at every temperature. 



3. Sulphurous acid gas departs notably from the la%v of dilata- 

 tion which the preceding gases present. The coefficient of dilata- 

 tion of sulphurous acid diminishes with the temperature as marked 

 by an air thermometer. 



It is important to remark that in these experiments the relative 

 dilatations of the gases were not measured directly, but were de- 

 duced by calculation from the observation of the elastic forces which 

 these gases present at the same temperatures, their volume remain- 

 ing constant. It appears very probable that similar conclusions 

 would be arrived at, by measuring directly the increase in bulk of 

 the different gases for the same temperatures, their elastic force re- 

 maining constant, by a method analagous to that of the fifth series 

 of experiments upon the dilatation of gases; but these experiments 

 would not be susceptible of equal precision in the measurements, 

 for reasons already given at the commencement of this memoir. 



f To be continued. J 



COPPER SMELTING FURNACE. 



A correspondent of the Mining Journal gives the following estimate for 

 the construction of a reverberatory furnace for smelting copper on the 

 Swansea plan. The stack of the furnace was single, 40 feet high, and the 

 furnaces 13 feet by 8. The following are the details : — 



12,000 common bricks— at 30s. per mille .. £13 



12 barrel! of lime— at 4s .. .. 2 8 



.•JiOOO NewcasUe bricks— at 3?. 10s. per mille, .. 17 10 



1,300 Dynas ditto— at 41. lOs. per ditto .. 5 17 



2,000 Stonrbridge ditto— at 8/. „ .. 16 » 



li ton cement clay— at 1/. 179. .. 2 15 G 



2 tons Dyna» ditto— at 15s. .. 1 10 



12 brown Flintshire bearers— at lOd. ., 10 



2 Stourbridge ditto— at Is. Id. .. 2 2 



6 8laba-at7d. .. .. 3 « 



23 c»st-lron atuds, 60 cwt.— at 7s. 6d. ., 18 15 



2 wrought-iron ditto, 2^ sq., 3 cwt,— at I63. 2 8 



3 sleepers, cast-iron, 3 sq., 5 cwt. — at 7s- 6d. 1 17 G 

 Hopper and frame, round iron for cramps, square 5-iron for 



stack rocks, flat 1 X 14 for stack cramps, fire-bars and 



wedges, about I ton— at 10/. 10s. .. 10 10 



Fore and concave and skimming plates .* 



Contingencies .* .. •• 



Making a total of 107 6 8 



To this must be added, about HI. for the masons' labour, and 21. for that of 

 the smiths', which, added to the cost of the furnace, 107/. 6s. 8</., will make 

 a total cost of 123/. 6s. Sd. The prices given are those of the period when 

 the furnace was constructed ; — of course, at different times they will vary con- 

 siderably ; any one, however, will be able from them to calculate what the 

 present outlay would amount to. By building two furnaces, with a double 

 stack to serve both, and using clay in the sides, instead of bricks, a less 

 consumption of materials would take place, which would necessarily be fol- 

 lowed by a commensurate reduction in the expenditure, thereby enabling 

 the contractor to construct his furnaces on a more economical principle than 

 above detailed. 



7 

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