1^44.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



319 



greatest capacity for heat. From this it is inferrred that bodies, though of 

 the same temperature, do not contain the same qxmntity of heat. The quan- 

 tity of heat requisite to raise bodies to the same temperature is called their 

 specific heat. A table of the specific heat of a few gaseous bodies is here 

 given : — 



Water 1-0000 



Air 0-2669 



Hydrogen gas 3-2936 



Carbonic acid gas .. 0-2210 



Oxygen gas 0-2361 



Table of specific heat of equal weights of- 



Nitrogen gas 0.2754 



Nitrous oxide gas ... . 02369 



defiant gas 0-4207 



Carbonic oxide gas . . 0-2S84 



Aqueous water 0-8470 



The compression of air diminishes its capacity for heat, and consequently 

 its temperature rises. A little piece of apparatus, called the tinder syringe, 

 has been constructed, by suddenly pressing the piston of which, a piece of 

 tinder is ignited by the heat evolved from the compression of the air. The 

 French girls in Paris are very dexterous vvitli this little instrument. The ex- 

 pansion of air, on the contrary, by increasing its capacity, produces cold. A 

 bottle of soda water, when opened is seen to smoke ; this is owing to the 

 sudden expansion producing cold enough to condense the aqueous vapour 

 previously invisible in the gas. A curious property with respect to heat has 

 been observed with India rubber; when forcibly drawn out considerable 

 heat is evolved, which is best observed by placing it against the lip both be- 

 fore and after extension. This may be repeated any number of times, but 

 this property can hardly be connected with its capacity for heat. 



The expansion and contraction of the atmosphere, and its consequent 

 change of temperature, is no doubt a very influencial element in the changes 

 which take place in the weather, and is an important consideration in the 

 science of meteorology. 



Heat bears a singular relation to electricity, which was first pointed out 

 by Seebeck. He found that when two metals were attached together, and 

 heated at their junction, a current of electricity was developed, which de- 

 flected the magnetic needle. The metals found most advantageous for this 

 purpose are bismuth and antimony. In the first lecture electricity was em- 

 ployed as a source of beat, now the converse, heat as a source of electricity. 

 A parallelogram of bars of antimony and bismuth, with the points of contact 

 alternately heated and cooled, will deflect a magnetic needle placed over or 

 under any part of it ; or by connecting the extremes with a galvanometer, 

 its action is more evident. The term thermo-electricity is applied to this 

 new collection of facts. Pelltier has added some curious observations on this 

 point. He has proved that when a weak electric current from a single cir- 

 cuit is transmitted through a bar of equal lengths of bismuth and antimony 

 soldered together, from the antimony to the bismuth, heat is evolved at the 

 point of junction ; but if the current is sent in the other direction, cold is 

 produced. A delicate thermometer inserted in a hole at the point of junc- 

 tion rises 80" in the first case, and sinks to 6" in the second. If the bar be 

 placed on thawing ice, a little water may thus be frozen in the cavity made 

 for the thermometer. Melloni and Nobili, by using groups of wires, and 

 connecting them with a delicate galvanometer, have constructed apparatus so 

 sensitive to beat, that the warmth of the hand held at a considerable distance 

 affects it, and it will even indicate the warmth of a silkworm crawling over it. 



But to return to vaporisation and its effects, which can be beautifully illus- 

 trated by means of carbonic acid. It has been shown that bodies evaporate 

 at different temperatures : thus a little ether poured into a bladder will fill it 

 with its vapour, whilst water would require a much higher temperature. 

 Carbonic acid, which is usually known only in the gaseous state, can be liquified 

 and even solidified by great pressure and cold. Cyanogen gas, discovered by 

 Gay Lussac, can be very readily liquified, and this can be efl'ected in the fol- 

 lowing manner. Place some cyanide of mercury in the body of a strong 

 retort, to the mouth of which is fastened a stop-cock; apply heat and the 

 gas will be liberated, close the stop-cock and the gas will accumulate in the 

 retort like high pressure steam, and when the pressure is about equal to four 

 atmospheres, the cyanogen becomes condensed into a liquid. Under similar 

 circumstances carbonic acid and many other gases may be liquified, though 

 most of them require very great pressures, as may be seen by reference to a 

 table previously given. The most striking properties of carbonic acid gas are, 

 that it is very dense, and extinguishes flame. Owing to its great density, it may 

 be poured through the air from one vessel to the other ; a little bucket let 

 down into an open-mouthed jar full of the gas may be drawn up full, as is 

 proved by a lighted taper being extinguished when inserted into it. Gene- 

 rated from carbonate of ammonia and sulphuric acid in a closed tube, it is 

 liquified when the pressure equals 47 atmospheres. [Mr. Faraday here exhi- 

 bited the original tube in which he first liquified carbonic acid, in the labo- 

 ratory of that institution, which was still charged with the liquid.] This has 

 been ably carried out by Thilorier, who constructed apparatus for collecting 

 it in large quantities ; but Mr. Addaras has constructed far more perfect 

 apparatus for that purpose. It consists of two exceedingly strong iron 

 vessels, in one the materials are placed for generating the gas, the other is 

 used as a receiver for the liquid produced in the first. Thilorier discovered 

 that when the hquid was allowed to rush into the air, part of it expanded 



nto gas, whilst the other part, from the loss of heat, which was absorbed by 



be gas, nas (tozen into a solid, This he collected in a (in box nitb per- 



forated handles to allow the gas to escape. In this state carbonic acid is a 

 snow-like substance, slowly vaporizing at ordinary temperatures. It can be 

 handled without annoyance, feeling cold to the touch, but leaving a sensation 

 hke hot iron. Its temperature is about 130" or 140" below 0°. If placed 

 in a retort with the neck immersed in water, the gas is slowly given off, and 

 is seen rising through the water. Placed at the bottom of a glass vessel, it 

 fills it with gas, which extinguishes a lighted taper. Laid on mercury it 

 abstracts from it but little heat ; and it may, like water, be placed on a very 

 hot metallic capsule and yet be but slowly evaporated, though the capsule be 

 red hot. This apparently contradictory fact, that a body so intensely cold, 

 and consisting of an immense quantity of gas, pent up, as it were, in small 

 compass bv that cold, should he scarcely affected by a red heat, arises from 

 the circumstance that it is continually surrounded by the vapour of its own 

 gas, which prevents it from touching the substances it is brought near, and 

 this gas being a very bad conductor, protects it likewise from external in- 

 fluences. But should a liquid be added to it which would wet it and the 

 substance experimented on, without at the same time being frozen by the 

 cold, then the properties of the soUd carbonic acid are developed. Ether, 

 Thilorier found, was such a liquid, as may be seen by pouring a little ether 

 on the solid acid resting on the mercury, which would have had little effect 

 on otherwise, but which now freezes the mercury to a solid state. A sauce- 

 pan may be frozen to a stool, as with the ice and salt. Glass vessels are in- 

 stantly cracked, owing to their suddenly contracting. The degree of cold 

 produced is intensely greater than mariners ever have experienced, and there- 

 fore any part of the body which was now touched with it would be perished. 

 It is said that Messrs. Pepys and Allen, by dint of a tedious process of cooling, 

 succeeded in freezing 40 lb. of mercury ; but with the solid acid this is easily 

 done. A piece of mercury frozen on the end of a stick, and held in some ice 

 cold water, is immediately covered with icicles, which shoot through the 

 water till it is frozen, at the same time the mercury is thawed and fall in 

 drops to the bottom, thus proving that water in freezing gives out heat. 



The next two lectures will contain the transmission of heat, and the na- 

 ture of flame. 



REGISTER OF NEW PATENTS. 



(Under this head we propose giving abstracts of the specifications of all the most ira- 

 portaDt patents as they are enroUed. If any additional information be required as to any 

 patent, the same may be obtained by applying to Mr. LAX'l'ON at the Office of tbla 

 JOURNAL.) 



MANUFACTURE OF GAS. 



Baptists Buret, mercliant, and Francois Maeius David, manu- 

 facturer of gas apparatus, both of Leicester Square, in the county of 

 Middlesex, for " ImprovementB in the manufacture of gas." — Granted 

 Jan. 30 ; Enrolled July 30, 1844. 



This invention consists in the peculiar construction of retorts to be 

 used in the manufacture of gas made from fatty matters, such as oil, 

 tallow, pitch, tar and other substances. The retort employed by the 

 patentees is of a cylindrical form, and made of iron or clay, and of the 

 ordinary construction with the exception of having a division plate in 

 the centre, which extends to within a short distance of the farther 

 end ; this retort is fixed in the brickwork in a vertical position and is 

 surrounded by a flue, the fire being below ; the cover or lid of the re- 

 tort is provided with two pipes, an inlet and outlet, the former pipe is 

 connected with a small tank or cistern containing the fatty matter, 

 which is kept in a fluid state by means of hot air from the fine, the 

 outlet pipe being connected with an arrangement of pipes which forms 

 the condenser. 



The pitch or other substance from which the gas is to be made, 

 when in a fluid state passes through the inlet pipe and is allowed to 

 drop on to red hot coke which is in the bottom of the retort, and the 

 gas evolved passes through the outlet pipe, and through the conden- 

 sers into the washing apparatus, which consists of a rectangular box 

 having a compartment filled with heath and sticks through which the 

 gas passes, and from thence into the gas holder, which completes the 

 process of manufacturing gas according to these supposed improve, 

 meuts. 



STEAM PROPELLERS. 



Robert HoDGso^f, of Princes Street, Clapham, in the county of 

 Surrey, for " Improvements in propelling vessels, and in machinery for 

 working the same." — Granted Feb. 2 ; Enrolled August 2, 1844. 



This invention consists in a peculiar mode of applying vanes or floats 

 to shafts for steam or other propellers. Fig. 1 is a geometrical figure 

 intended to illustrate or show the proper position to be given to the 

 vanes or propellers, presuming the propellers to be made, are intended 

 for the stern of the vessel ; it will be necessary, in the first place, to as- 

 certain the diameter of the largest circle which can be described 

 within the space intended for the reception of the propellers : sup- 

 pose, for instance, « {) tQ be the radius, then vvUh ^wh radius.desctibe 



