S C I E K T I- 



I 



Srice. > vessel CD. When the ga* is thus collected in the ve- 



tle * sel CD, a stream of it may at any time be discharged 



. through ihe aperture c, and thrown upon the spunky 



platinum I', when it will produce ouch an intense heat 



as to make the platinum red hot, and thus afford an in- 



stantaneous li:;!it. 



In Mr. (i.inlcn's lamp, the ringof ziur op flosts up- 

 on a piece of cork, so that when the vessel CD is filled 

 with gas, the dilute arid does not touch the zinc, and 

 consequently no more hydrogen is produced ; but the 

 moment any of the gas is let off at r, the pressure of 

 the head of fluid in AB overcomes the elasticity of the 

 remaining gas in CD, and the diluted acid in forced up 

 to the zinc, to reproduce the wasted hydrogen. 



By this ingenious contrivance, the diluted acid is 

 I ti'-si-d up against the zinc when more hydrogen is 

 wanted, and withdrawn from it when the vessel CD is 

 full. 



The form given to the lamp, by Mr. Adie of this city, 



Via-. S. is shown in Fig. 3. No. 2. where the different parts are 



No. 2. marked by the same letters as in Fig. 3. In this con- 



struction, a cone of glass k formed on the bottom of 



the vessel AB is made to hold the ring of zinc, op, 



which remains permanently in thnt position. This 



lamp has the advantage of greater stability, and is less 



liable than the other to be deranged by an accidental 



cause. 



Professor Cumming of Cambridge, who constructed 

 one of these lamps in December 1823, found it neces- 

 sary to cover up the platina with a test tube, cr a cap, 

 after every experiment. With platina foil JT^T ^ an 

 inch in thickness, and kept in a close tube, he produc- 

 ed the same effect ; but when the thickness of the foil 

 was 5 j', 7 , it was necessary to raise it previously to a 

 red heat. 



These lamps, besides their extreme beauty as philo- 

 sophical toys, are of great use in counting houses, as 

 well as in private houses, in summer, when there is no 

 fire at which a taper can be lighted. 



10. Lamps without Jlame. 



A lamp without flame which was first constructed 

 by Mr. Ellis, has been already fully described in our 

 article LAMP, Vol. XII. p. 509- As no drawing of it 

 is given under that article we have thought it proper 

 to represent it in Plate CCCCLXXXV, Fig. 4, where 

 ^g j s ^ j am p containing ether or alcohol, and h the 

 coil of platinum wire the hundredth part of an inch 

 thick. A thin sheet of platinum or palladium will pro- 

 duce the same effect. 



11. Dobereiner's natural lamp by Incandescence. 



In using a spirit of wine lamp, M. Dobereiner ob- 

 served, that when the spirit of wine was nearly con- 

 sumed, the wick became carbonised, and though the 

 flame disappeared, yet the carbonised part of the wick 

 became incandescent, and continued red while a drop 

 of alcohol remained, provided the air in the apartment 

 was tranquil. In one experiment it continued red 

 twenty-tour hours; a disagreeable acid vapour, how- 

 ever, was formed. 



Dr. Brewster long ago observed an analogous fact in 

 the small green wax tapers in common use. When the 

 flame is blown out, the wick will continue red tor 

 many hours, and the wax and wick are burned down 

 as in it? ordinary combustion, only with extreme slow- 

 ness; a very disagreeable vapour being formed during 

 the imperfect combustion. Dr. Brewster has observed 

 also that the same effect is not produced when the ta- 



TOL. XVII. PART II. 



1/atr.ps 

 without 

 flame. 



PLATE 

 CCCCLXXXV 

 Pig.*- 



inouides- 

 <. 



per i made of red wax. This probably arises from th 



coin ,rin...' matter of the two taper*. There can be lml<- ' 



doubt, however, that the -ame result will be obtained 



with different kind* of wax, and even with Ullow, *-' 



provided the quantity of wax if properly proportioned 



to the diameter oi the wick. 



1 2. On the Ino ntM Fluidt in the catitift of gemt. 

 Two new fluids, possessing extraordinary physical O ihr i* 

 properties, have been recently discovered by Dr. ne1 ".*"'** 

 Hri'wster. in the crystallized cavities of gems, a* topaz, J? 

 quartz, arncl/itjtl, and chrytofaryt. These cavities fre- 

 qumtly occur in millions in a single specimen, and 

 they are often so minute as to escape the cognizance of 

 the highest magnifying powers. 



The two fluids are in general perfectly transparent 

 and colourless, and they exist in the same cavity, in 

 actual contact, without mixing together in the tlightest 

 degree. One of them expands thirty times more than 

 water ; and at \ temperature of about 80 degrees of Fah- 

 renheit, it expands so as to fill up the vacuity in the 

 cavity. When the vacuity is large in proportion to 

 the quantity of fluid, a little addkional heat converts it 

 into vapour, which exhibits, in its formation and con- 

 densation, a series of beautiful optical phenomena. 

 This fluid is also singularly voluble, so that a cavity 

 with rectilineal sides forms a most delicate microscopic 

 level. 



The secMid fluid, which invariably accompanies the 

 first, is not more expansible than common fluids. It 

 occurs in smaller quantities than the first fluid, and has 

 a higher refractive power. 



Dr. Brewster has succeeded in taking these fluids 

 out of their cavities, and in examining their properties 

 when exposed to the open air. The first fluid con- 

 tracts and expands in the most rapid manner, as if it 

 consisted of particles endowed with vitality ; and both 

 of them indurate into a sort of a resinous substance, a 

 state in which they often appear even when they are 

 imprisoned in their cavities. 



The existence of these two fluids to such an extent 

 in minerals, and their occurrence with precirely the 

 same properties in specimens brought from such oppo- 

 site regions as Scotland, Siberia, New Holland, Brazil, 

 and Canada, renders it probable that they have per- 

 formed some important function in the mineral organi- 

 zations of our globe. 



In order to give the reader some idea of the ap p LAT c 

 pearance of these two new fluids as coexisting in theccccuxxxr. 

 same cavity, let AB, Plate CCCCLXXXV, Fig. 5, re- Fig. 5. 

 present one of the cavities in topaz as seen through a 

 microscope, or even by the naked eye, (for some of 

 them are sufficiently large to be seen by the naked 

 eye) then there will be observed a circular vacuity V in 

 the fluid EF, and the fluid EF will be seen bounded 

 by two lines m n, o p which separate it from the other 

 fluid CD. When the heat of the hand is applied, or a 

 heat so low as 74, the vacuity V gradually grows len 

 from the expansion of the fluid EF, and it soon disap- 

 pears. The fluid CD, however, is not all perceptibly 

 expanded by the same heat, as appears from the bound- 

 aries m , o p remaining stationary. When the topaz 

 cools, the fluid EF contracts, and the vacuity V re-ap- 

 pears and enlarges. If the cavity is deep, the vacuity 

 V re-appears with a violent effervescence, but the va- 

 rious vacuities or bubbles thus formed speedily unite into 

 one. When the cavity is shallow the vacuity V often r*. 

 appears in two or three vacuities which unite into one. 

 The refractive power of the expansible fluid EF is 

 4 c 



