1847.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



85 



surfaces were uneven and ruffled, by the metal plunger not always being 

 kept sufticiently hot. An ingenious cylindrical vial mould, for blowing 

 bottles wilhoiit seam, of uniform sizes, was used ; and bottles were manu- 

 factured both from it and the ordinary open and shut moulds, which will 

 be polished and clean blown, provided the inside of the moulds are kept at 

 Dearly the same heat as the temperature of the glass blown in them. The 

 elasticity of glass was exemplified by glass balls of about three inches dia- 

 meter rebounding from a polished iron slab (hree-fuurlhs of the heisjht from 

 ■which tliey were dropped, as well as by blowing glass so attenuated as to 

 be sustained some short time floating in the atjnosphere ; this is technically 

 called glass frost. Annealing and its eli'ects were briefly stated. The 

 process of casing (called by the French double, Irehh, &c.) colours upon 

 ■white glass was then practically shown by the workmen, who covered a 

 white glass toilet-bottle with blue, about the tliickuess of an eggshell ; 

 and Mr. Pellatt displayed a vase of the exact size and shape of tlie Port- 

 land vase, manufactured at the Falcon Glassworks with a thick interior 

 coating of dark blue glass, upon which a thin white enamel of glass casing 

 ■was laid ; his engraver had cut away parts of the white, leaving uiasses 

 of blue in the neck and upper part of the vase exposed to view, and had 

 chased out at the lathe, with the engraving tool, a portion of the bas-re- 

 lief. 



A full size drawing of a double-handled vase, without foot, now in the 

 Museum of Naples, was exhibited, made of blue glass, and cased with 

 white enamel, with handles, from which were engraved in relief, an elabo- 

 rate arabesque subject, with a group of Bacchanalian boys under each 

 handle. In design and artistic power it is considered by Zahn as second 

 only to the Portland vase. This vase was found in Pompeii in the year 

 IS37. Mr. Pellatt stated that Mr. VVigel, the celebrated gem-engraver, 

 had expressed a desire to make an exact copy in glass of the Portland 

 vase, provided he could set apart adequate professional time for the object; 

 and Mr. P. expressed his determinalion to aid this patriotic intention, 

 pledging his Firm to its execution, so far as regarded the manufacture of 

 the crude vase. This species of engraving in relief, probably took its rise 

 among the Greek and Roman artists, in imitation of reil bas-relief gems. 

 Many rough and unfinished specimens are to be seen in the British Museum. 

 Modern engravingof rough patterns upon transparent glass cannotbe traced 

 earlier than the Venetians. A lathe, a ci.pper wheel and emery-powder 

 for the rough grounds, and a lead wheel for polishing, are the engraver's 

 tools. Specimens were on the table, as worked by the lalhe. Glass-cut- 

 ters' iron wheels for cutting, used with wet sand ; stone wheels, used for 

 smoothing with water, and wood wheels for polishing with pummice, and 

 afterwards with putty powder, were slightly explained from the specimens 

 exhibited. Flint-glass decanters, roughed, smoothed, and polished, were 

 shown ; also four polished cut decanters, of one uniform shape and size, 

 but varying in strength, to exemplify the ditl'erence of brilliancy ; that with 

 ten faces of flutes on the cylindrical body being least refract iie, and that 

 with six faces or fluting being most refiaclive ; and the eight tinted and ten 

 fluted ranging between the two extremes in refractive efl"ect ; the condition 

 of pellucid refractibility depending upon the greatest projection of angle, 

 in proportion to the greatest quantity of flat surface cut away from the ex 

 terior of the cylinder (the interior remaining circular). The last glass 

 manipulation of the workmen was drawing Venetian filigree cane. Threads 

 of white and coloured glass were placed vertically around the extremity of 

 the interior of a brass mould ; a solid flint-glass ball was blown into the 

 interior of the threads, welding the latter to the outside of the ball, and 

 drawn as tube and cane is usually drawn, except that each workman 

 twisted in an opposite direction, as they retired from each other to lengthen 

 and attenuate the filigree cane; which, being whetted oQ'into such lengths 

 as may be required, is afterwards used for wine-glass stems, or made up 

 into vases, paterae, and other filigree objects of taste. Specimens of mosiac 

 glass were also shown and explained, by which, pictures, as described by 

 AVinkelman, were made, by welding lengths of small cane to each other, 

 the patterns being previously sectionally arranged to required variety of 

 colour, &c. ; so that when massed together by fusion, the whole shall ap- 

 pear homogenous. These are cut ofl' into slabs at right angles to the length ; 

 so that the subject or pattern is repeated on each slab. Venetian milleliore 

 glass was explained to consist of single canes of filigree glass, cut olf into 

 small lozenges, and placed side by side, and welded to while Dint-glass, 

 forming a sort of mosaic work. The manner of making schmellz and rltro 

 de trino was slightly alluded to, and Mr. Pellatt stated that he had tried 

 to imitate the projecting crystal forms divided by concave fissures 

 of the Venetian frosted glass, and had failed, as he had plunged the 

 manufactured article while hot into cold water, which only dislocated the 

 interior particles of the glass, leaving the surface nearly smooth ; whereas 

 his friend Mr. Green had chilled the glass in water in the earlier process 

 of the manufacture, which being afterwards rewarmed at the furnace and 

 expanded by blowing, separated ihe crystals from each other, leaving the 

 fissures between identically with the Venetian ; apparently full of fractures, 

 but really whole and entire. The enclosing of cameos in shut-up pockets 

 was explained. A beautiful specimen of pedestal, with a caryatides en- 

 closure in solid glass, also bricks of glass, with written and composition 

 inscriptions incrusted, were on the table. 



Mr. Pellalt concluded by bearing public testimony to the workmen for 

 their willingness and success, notwithstanding the short time of fusion, 

 and the comparative incompleteness of the furnace; and by sincerely thank- 

 ing the possessors of ancient glass who had kindly lent him specimens, or 

 given him access to their collections. 



ON THE NATURE OF HEAT. 



Mr. Grove gave a lecture at the Royal Institution, Feb. 5th, on "some 

 Considerations of Ihi Nature of Heat" — After a sketch of the existing 

 theories of heal — the emissive, the ethereal, and the dynamic — Mr. Grove 

 announced himself an advocate of the last, viz. that which regards heat as 

 molecular motion of ordinary matter. The phenomena of what is called 

 " latent heat" have always been considered a stumbling-block in the way of 

 this theory, and a strong argument for the materiality of heat. Mr. Grove 

 considered that all the phenomena of latent beat might be accounted for 

 more simply by the dynamic theory, and that the greatest difliculty in apply- 

 ing this theory was the necessity of excluding ideas associated by long usage 

 with the phenomena, and also of employing terms which had become en- 

 grafted by custom on the expansive effects of heat. Thus, in expounding a 

 new view, although more simple in itself than the received ones, we are 

 obliged to avail ourselves of received terms, to which, while we use them, 

 we object. Excepting the case of certain substances which expand in freez- 

 ing, and which expansion is accounted for by their crystallisation, making 

 the body occupy more space, by leaving interstices between the crystals, Mr. 

 Grove stated that all the phenomena in which the so-calltd latent heat is 

 concerned were mere expansions and contractions ; and that what, according; 

 to that theory, would be called absorption of heat, was mere extension of 

 the substance said to absorb the heat. Thus, suppose a given quantity of 

 water to be heated by a given quantity of mercury; the first effect is, that 

 the water expands, the mercury contracts ; at a certain point, viz. that at 

 which the water is said to have reached its boiling point, the attraction of 

 the molecules of water is so conquered by the repulsive force, heat, that the 

 water bursts into vapour ; here its molecules being more separated, and 

 having consequently a less attractive force, are so much more readily ex- 

 panded, and exhaust much more expansive force from the heated mercury: 

 this, therefore, loses expansive force, i.e. contracts or shrinks ; and the more 

 so in proportion to the readiness of expansibility of the substance which 

 robs it of its expansive force. So, if the calorific force be supplied by other 

 means, such as ordinary combustion, say of coal and oxygen, i. e. chemical 

 action, the expenditure of fuel will be in proportion to the expansibility of 

 the substances heated ; so that the same quantity of water will require the 

 same quantity of heat to convert it into steam, whatever the pressure. 



If, again, the same source of heat he applied to the two substances, water 

 and mercury, say to a thermometer immersed in water, both gradually ex- 

 pand, but in different degrees ; at a certain point the attractive force of the 

 molecules of the water is so far overcome that the water becomes vapour;, 

 at this point the heat or force, meeting with much less resistance from the 

 attraction of the particles of steam than from those of mercury, expends 

 itself upon the former : the mercury does not expand, or expands in aa 

 infinitesimally small degree, and the steam expands greatly ; as soon as this 

 arrives at a point where circumambient pressure causes its resistance to fur- 

 ther expansion to be equal to the resistance to expansion in the mercury of 

 the thermometer, the latter again rises ; and so both go on cxpaniiing in aa 

 inverse ratio to their molecular attractive force. Again, if the steam he not 

 allowed to expand, as by confining it by a less expansive body, say a metallic 

 chamber, then the mercury of the thermometer immediately rises. Thus 

 heat is regarded as a purely mechanical efl'ect ; and indeed it can be made to 

 reciprocate with mechanical action. If by mechanical pressure we cause a 

 substance to contract, this gives out heat, i.e. causes surrounding bodies to 

 expand ; and, vice versa, if we mechanically rarify or expand a substance, 

 cold is produced, i. e. contraction in surrounding bodies. The theory was 

 also applied lo the increase of specific heat iu bodies as their temperature 

 increases, and to many other points ; and the whole subject was experiment- 

 ally illustrated. 



Mr. Grove next passed to the consideration of the effects of heat, viewed 

 as repulsive force, upon another mode of molecular attraction, viz. chemical 

 aflinity. A vast number of compound bodies are decomposed or resolved 

 into their constituent elements by heat ; and these effects may be accounted 

 for by supposing that heat so far separates their molecules as to remove them 

 from the spheres of their afSnity. In other sulistances, however, chemical 

 combination is produced by the application of heat ; and though by certain 

 hypotheses these latter effects may also be accounted for by the repulsive 

 action of heat, Mr. Grove seemed to consider these hypotheses rather strain- 

 ed. Water has, up to a recent period, been considertd not only undecom- 

 posable by heat without the aid of some other powerful chemical affinity, 

 but the elements of water are united by the action of heat; and in pneuma- 

 tic analyses heat has hitherto been employed to combine the elements of 

 water with each other, or with other gases. Mr. Grove however has proved, 

 and experimentally showed on this occasion, that water is capable of being 

 decomposed by beat; thus forming no exception to the general antagoniam 

 of beat and attractive force. 



