20 On Camphor Pulsations. 



you do not seem to have apprehended me fully, or I may not 

 haw expressed myself clearly. My theory is that light has 

 nothing to do with the deposit of camphor, of vapours, or of 

 crystals of saline solutions on the most illuminated side of the 

 glass vessels that contain them, but that such deposits are formed 

 by condensation on the coldest side of the vessel, -which may 

 or may not be the most illuminated side. If a number of 

 bottles containing a little camphor, naphthaline, iodine, water, 

 turpentine, etc., be placed in the window, the deposits will be 

 formed generally on the side nearest the light, because that side 

 is generally the coldest ; but if the sun be shining on the win- 

 dow, the side nearest the light will be the hottest, and the de- 

 posit will go to the back of the bottle, or to the coldest side, 

 if the bottle be equally heated in every part, and equally 

 cooled, no deposit will be formed except at the bottom of the 

 vessel, unless the cooling be sufficiently rapid and great to con- 

 dense the elastic vapour as it subsides. We shall then have a 

 deposit equally all round the glass, and this is the more likely 

 to happen with a thin one, because glass being a bad conductor 

 of heat, a thick narrow glass is not so likely to cool unequally ; 

 it does not, in fact, present a cold side and a warmer side, unless 

 under favourable circumstances. For instance, a thick baro- 

 meter tube containing a charge of camphor was left in one 

 corner of a warm room, it was afterwards exposed to the cold 

 of winter, and when next examined it was found to have a 

 deposit equally all round. It will, of course, be understood 

 that under all ordinary circumstances a bottle containing cam- 

 phor, etc., is filled with the vapour of that substance at all ordi- 

 nary temperatures. A certain depression of temperature is 

 required to cause a deposit, as in the case of dew, and unless 

 tho temperature be sufficiently depressed there will be no 

 deposit. In vacuum, the camphor deposit may be formed in a 

 few minutes, as in Dr. Draper's experiments, and it was to get 

 rnl of the cumbersome machinery of air-pump, and air-pump 

 receivers, that I made use of the more sensitive crude camphor, 

 whi.l, forms a good deposit if a little of it be placed at the 

 bottom of an ordinary corked vial. So sensitive is this vapour 

 of crude camphor that it will revive marks, and small impuri- 

 iii tin- bottle, the presence of which was not suspected. 

 The minute invisible filaments left by the duster used in wiping 

 out the bottle, bccomo visible in a few minutes after the bottle 

 has received its charge; of crude camphor, and exposed in the 

 window in consequence of becoming coated with that substance 

 condensed upon mem. 

 Kare'i Oonaaa, London, 



lUh June, 18fi;j. 



