ZTi^ Experiments with the Lamp Furnace. 



ih* ring which fupports the vefle], or the bodyof the lamp if tile vefltls Be-fixed iir communi- 

 cation with otliers, I graduate the heat>at pleafure. V inegar diftils without interruption at 

 fix centimetres (a-J- inches Eng'ifti) from the upper termination of the chimney, that is to fay, . 

 at igcfentimetres (7|. inches Englifli) from the flame. Water is made to boil in eight- 

 minutes, at the fame height, in a glafs vefl'el containing five decilitres (one wine pint Englifli),, 

 and is uniformly maintained at the diftanoe of twenty-two centimetres (8y inches) from fhe 

 flame. It will foon be ftiewn, that T have another method of fupplying chemifts v^ith < 

 dilUlled water; fo that I fcarcely ever repeat this operation but when I have no other fup- 

 ply at hand, or am defirous of avoiding all trouble whatfoever. In this cafe, I obtain two or 

 three decilitres (or quarter pint?) of water in the courfe of a winter eveningj without the 

 leaft portion of my time being employed in attending to the operation. 



I muft not in this place omit to mention a flight obfervation which this procefs has afforded, . 

 becaufc it may Icadto ufeful applications, and tends to point out one great advantage of this, 

 method of operating ;. namely,, that an in.'iaity ofcircumftances 'may be perceived, which 

 might not even be fufpected when the whole procefs is carried on within arfurnace. I have 

 remarked, as did likewife feveral of my colleagues who were ther* prefent, that a column . 

 of bubbles conftantly rofe from a fixed point of the retort on one fide of the bottom. We 

 were of opinion, that fome particle of matter was in that, place incorporated with the glafs, , 

 which had a different capacity (probably condufbing power) for heat from that of the reft of 

 the glafs. In order to verify this conjeclure, I endeavoured the following day to diftil the 

 fame quantity of the fame water in the fame retort, after having introduced a button of 

 cupelled filver, weighing nine decigrammes (20^- grains).- At the commencement of the 

 operation there was a fmall ftream of bubbles from the fame point as before; but a (hort 

 , time afterwards, and during the whole remaining time of operating, the largeft and moft in- 

 cefiant ftream of bubbles rofe from the circumference of the button, which was often dif~ 

 placed by the motion; and in proportion to the time the produ£t of the diftillation was 

 fenfibly greater. Whence we may conclude, that metallic wires or rods, diftributed through 

 a maft of water required to be kept in a ftate of ebullition, and placed a-little below"its fur- 

 fece, would produce, without any greater expence of fuel, nearly the fame efFed as thofe 

 cylinders filled with ignited matter which are made to pafs through the boilers *. 



It now remains tofliew the economical method of fupplying the water neceflary for expe- 

 riments. 



When water is mentioned in chemiftry, pure water is always meant. In medical prc- 

 fcriptions it is ufual to prefcribe fpring water, though in many places the water of fprings or 

 ftreams is more loaded with felenite or fidphate of lime than the well water of other places. 

 The fame remark may be applied to river water, which is no doubt more wholefome thaa 



• When we attempt to reafon on this curious fa£l of the metallic buKon, there are various circumftances 

 which require to be confidered. It does not feem probable, that a larger quantity of a fluid. can be rendered 

 elaftic by a given quantity of heat, unlefs we fuppofe part of the heat to have been wafted in the former pro- 

 cefs. Does the metal, by the excellence of its condufting power, convey a portion of the heat more readily into 

 the mafsof liquid than might have been done by the ordinary procefs of circulation ? Or is the thin ftratum be- 

 neath the button fo far infulated as to become morefuddenly elaftic, and, by riling in that ftate to the furfece, 

 to increafe the rapidity of circulation, and the number of points at which vapour can efcape ? Would a tuft of 

 filver wire produce the fame e&ft,? &c. &c. N. 



