Answers to Queries. ISI 
salt in 16 parts of water, to which 1 part of diluted sulphuric acid 
(1:8) is added. A few minutes’ immersion in the solution makes 
the negative clear and colourless.— Photo. Times. 
Answers to Queries. 
342.—Chill at Sunrise.—-The earth is naturally coldest just 
before the sun has risen, having then had longest to cool. When 
the sun begins to warm the earth, the overlying air, becoming heated, 
ascends, and cold air rushes into its place from the parts not 
already warmed by the sun, thus producing the cold wind spoken 
of by your correspondent. MATHEMATICUS. 
364.—Removing Grease.—Soak the insect thoroughly with 
benzine, and then sprinkle French chalk all over the body and 
wings. At the end of half-an-hour, the chalk may mostly be 
blown or shaken off, the remainder being carefully removed with 
a soft camel-hair pencil, moistened, where necessary, with benzine. 
MATHEMATICUS. 
365.—Divergent Series.—No recognised name has been given 
to a series, the differences between the terms of which (or the 
differences between the differences, and so on) are in arithmetical 
progression. 1D Da sb 
365.—Divergent Series.—No method has ever been discovered 
for finding the sum or value of a divergent series of increasing 
terms, alternately positive and negative. EL. A 
367.—Sun putting out the Fire.—This is mainly an optical 
delusion, the less brilliant flames of the fire being rendered 
invisible by the far-greater brightness of the sun’s rays. But it is 
just possible that the sun, by heating the surrounding air, prevents 
the proper draught of air being formed, and thus deadens the 
combustion of the coal. Gari: 
370.—Specific Gravity.—How much water must be added to 
commercial strong solution of ammonia (NH, OH) sp. gr. ‘880, to 
give it a sp. gr. of ‘891? 
‘891—'880—ol1 dif. in sp. gr. between mixture and ammo- 
nia ; 1'°000o—’880= "12 dif. in sp. gr. between H,O and ammonia; 
OTT 09%. 
‘120 
.*. 9% parts of mixture is water ; or, 
pie og = (1 O)f 
109% 655 131 ete HO 
. +. 8% per cent. (H,O) of the amount of ammonia added to 
the ammonia solution will give the required sp. gr. Bele 
