244" Queries ajid Ans'xers. 



returned upon the caoutchouc. Those who cannot provide such an appa- 

 ratus may effect the same purpose in a large [)hial bottle, by loosely corking 

 it, and carefully applying the heat. The Indian rubber very soon dissolves ; 

 and, as different specimens require various quantities of ether for complete 

 solution, the best way is to make small additions, until a saturated solution 

 is obtained. The reason caoutchouc will not dissolve properly in sul- 

 phuric ether is in consequence of its containing some alcohol, from which 

 it requires to be freed by repeated washing ; for alcohol not only will not 

 dissolve Indian rubber, but will actually precipitate it from its ethereal 

 solutions. The solution in pyroligueous ether, when well made, is colour- 

 less and transparent, the impurities of the caoutchouc being always left 

 behind. The varnish, when saturated, must be applied with great rapidity 

 and evenness of stroke, otherwise it clogs. When it remains tuskey or 

 clammy, the varnished article should be exposed to a current of steam ; 

 which soon carries off the ether, but leaves the caoutchouc unacted upon ; 

 and firmly cohering in its solid state. A solution of Indian rubber may also 

 be made in Cajeput oil, which, for some purposes, promises advantages 

 over that in ether. Turpentine is a bad solvent of it ; but, when used, the 

 application of the current of aqueous vapour will always dry the varnish. 

 For the purpose of varnishing cord, or other coarse matters, for hor- 

 ticultural or other uses, the solution of the Indian rubber, in pyroligueous 

 ether, may be mixed with an equal bulk of drying oil, and the matters to 

 be varnished either dipped into it, and drained out, or brushed over. I 

 shall be happy to give your correspondent any further information in my 

 power; and am, Sir, yours, &c. — Robert Mallet, Capel Street, Dublin. 

 December, 15. 1832. 



On jireserving Cape Heaths from Mildeiv. (Vol. VIII. p. 736.) — Sir, I 

 have an extensive collection to attend to, and, perhaps, for a private collec- 

 tion, the first in England. My mode of treatment is as follows : I keep 

 them in the green-house both summer and winter ; I take especial care 

 that their tops never get wet, and also that the branches are kept clear from 

 damp, dead leaves, insects, and all other kinds of filth attendant on decayed 

 leaves, &c. ; and for this purpose I use a sm.all brush, such as painters 

 usually paint windows with : I use it quite dry, and as often as necessity 

 requires; I find, from experience, that the natural consequence of the 

 neglect of this treatment is the mildew, particularly in low situations. If 

 one of my plants happen to take the mildew, I immediately remove it into 

 a separate house, quite apart from the others, or into a cold frame ; for, if 

 it were suffered to remain, it will infect every plant in the heathery, and in 

 time destroy the whole. I then take a little flour of sulphur, and mix with 

 it a little soot, when it will become of a dark green colour (sulphur alone 

 would do just as well, but it is not so pleasant to look at to a delicate eye). 

 I then put it into a tin box, that has got a lid perforated with small holes, 

 or what is commonly called a flour duster ; I dust the whole of the plant 

 with this mLxture ; and, if this dusting has not the effect of removing it (and 

 sometimes it is a long time in clearing the plant ; I have had plants under 

 this operation for three months), you may take the pot, and lay it on its 

 side, so that the branches will lie on the ground, and then take a syringe, 

 and wash the plant well ; afterwards place it in a situation where the wind 

 will dry it quickly, then dust it as before. This last mode can only be 

 practised safely in dry and wai-m weather. I hope these few hints will 

 prove useful to R. W. (\ol. VII I. p. 736.), and others of your readers. I 

 am Sir, yours, &c.— A Constant Reader. Mancliestcr, Feb. 23. 1823. 



Alildew in Cape Heaths ; Causes and Prevention. — In reply to R. W.'s 

 query (Vol. VIII, p. 736.), I may state, the principal causes of mildevir 

 amono- Cape heaths are, first, exposing the plants, whilst out of doors 

 during summer, to the mid-day sun ; and, secondly, the pots getting over- 



