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POPULAR SCIENCE REVIEW. 
of a gall, which consists of new cells holding a mass of nutritive matter 
(particularly fecula) destined, not for the wants of the plants itself, hut for 
the development of the small parasite which appears. The production of 
gum at expense of the nutritive matter has no other limit than the com- 
plete exhaustion of the plant. Scarification of the hark is the best remedy. 
Mr. Prillieux’s explanation is this : — To cure the disease the materials mis- 
appropriated to formation of gum must he brought hack to their normal 
destination. Hence a more powerful attraction for them must be introduced 
than that of the gummy centres. Now the wounds of the bark necessitate 
the production of new tissues, and under this strong excitation the reserve 
matters are employed in formation of new cells, and cease to he attracted in 
the wrong direction. (See also Chemical Nevjs, June 19.) 
Prepared Paper a Test for Urea . — An article on this subject has 
appeared in the “ Comptes Bendus,” by M. Musculus. The following is a 
brief abstract of the method of using the paper as a qualitative test. 
Urine, when it has arrived at full alkaline fermentation, is thrown upon a 
filter. The pores of the paper are soon filled up with globules of a certain 
ferment, and the filtration slackens. The paper is then washed with dis- 
tilled water till the alkaline reaction has disappeared, and dried at a tempera- 
ture of 35° to 40° C. In this state the paper is an efficient test for urea, 
which, if immersed even in a very dilute solution for ten or fifteen minutes, 
it converts into carbonate of ammonia. The test-paper should be coloured 
yellow with turmeric. It is then dried afresh, and preserved in a stoppered 
bottle. If a slip of the paper is soaked in a solution of urea containing 
only Y^—th part, it soon becomes covered with brown spots. If it is re- 
quired to detect urea in a liquid, it must first be neutralised. If alkaline 
carbonates are present, acid enough must be added to decompose the bicarbo- 
nates which may be formed. These salts might induce an error. They do 
not immediately colour turmeric paper brown, but after the lapse of a little 
time the brown tint appears, especially on exposure to the air. Neutral 
alkaline salts do not interfere. The fermentation proceeds as well in the 
presence of phenic acid as in its absence. The quantitative determination 
of urea may be also performed with this paper. 
Is Turacinfrom the Touraco f — We are glad to see that Professor Church’s 
well-known researches on this peculiar colouring matter have been again 
completely confirmed. M. J. J. Monteiro, in the “ Comptes Kendus,” 
fully confirms the results of Church as to the presence of copper in the 
feather of the Touraco. Copper exists in the regions inhabited by the bird, 
in the state of green carbonate (malachite). 
Sow Soluble in Water is Arsenious Acid f — This question is answered 
in a late number of the “Bull, de la Soc. Chim.,” by M. L. A. Bucher. 
He says that 1 part of crystalline arsenious acid dissolves, after 24 hours’ 
digestion, in 355 parts of water at 15° C. The amorphous acid, in the same 
conditions, requires 108 of water. If the crystalline acid has been dissolved 
at a boiling heat, and the solution left to stand for twenty-four hours, it 
contains to 1 part of acid 46 of water. The amorphous acid, in the same 
circumstances, remains dissolved in 30 parts of water. 
How to form Octahedral Crystals of Borax. — M. Gemez says it is known 
that borax forms two hydrates — the one containing 5 equivalents of water, 
