ON THE MILDEW OF PLANTS. 
289 
to one of them, the taste may be found saline and disagreeable, but 
no unpleasant effect will be produced on the tongue. Then let him 
powder and dissolve it in as much boiling water as will, stirring with 
a tea-spoon, render it fluid. To this solution—kept boiling hot—let 
a tea-spoonful or two of powdered quick-lime be added ; and in a very 
few seconds a change will be perceptible; for, on applying the minutest 
drop to the tongue, a burning pungency will be discovered. In fact, 
were the process carried on till all the neutralising carbonic acid were 
taken from the soda by the lime, the skin of the tongue would be 
destroyed, and a wound created by any incautious application of the 
liquid. Things being in this state, let a little sweet (olive) or other 
oil be poured into a phial with an equal quantity of soft water, then 
add a few drops of the caustic soda liquor, and agitate the contents of 
the phial. If due proportions be employed, an emulsion , as it used to 
be termed, will be formed ; but, chemically speaking, soap will be 
produced by the union of the caustic soda with the oil, though it will 
be in a fluid state, being held in solution by water. 
Now, in testing the efficacy of soap in the cure of mildew, the fore¬ 
going and other processes should be performed ; and I shall shortly 
show that thereby the questions I proposed may be completely solved. 
Soft soap, the substance chiefly employed and recommended by gar¬ 
deners, is not a combination of soda and greasy matter: in the prepa¬ 
ration of this useful material, caustic potash is substituted for soda ; 
and they who are so inclined, may operate with these two materials in 
the manner above recommended—that is to say, mild potash (called 
carbonate of potassa) may be tried in solution upon diseased leaves: 
this solution may be deprived of the neutralising acid, and rendered 
caustic by the addition of quick-lime, and then it will combine with 
oily substances. 
Thus I have collected together materials for a course of experiments, 
and it remains to mention how far I myself have been able to proceed. 
I stated at the commencement of this article, that I had discovered the 
mildew upon one or two solitary laterals of apple-trees : to these I 
applied chemical agents thus prepared. One ounce of the crystals of 
soda was dissolved in seven fluid ounces of water: the taste of this 
liquor was far from potent: I plunged the diseased Twig into it over 
night, but did not leave it immersed for one minute. On the following 
morning every leaf was found killed, and of the colour of rust of iron. 
I rendered the solution slightly caustic by the addition of a few small 
pieces of very inert lime, not using any heat. The taste became 
slightly pungent; and I then diluted one fluid ounce with three ounces 
of rain water. Another twig was tested in a similar manner with the 
VOL. IV.-NO. L. 
G G 
