Queries. 799 
424,--Book on Minerals.—Could anyone give the name, price, 
etc., of a good book on minerals, giving formule, reactions, and 
other data ? F. W. STEEL. 
426.—Decolorising and Staining Leaves.—Can you tell me 
the dest plan of decolorising and staining leaves, so as to show 
their structure ? Ess: 
427.—Aquarium.—Shall be very glad to have any practical 
hints as to starting a fresh-water aquarium, or advice as to best 
books on the matter. ass 
428.—Mounting Crystals.—Have taken great interest in the 
subject of Crystallography, and have very successfully mounted 
several specimens. ‘The difficulty I am in, however, is, that some 
salts do not mount well in balsam. I have temporally mounted 
some in castor oil, and am delighted with their beautiful appear- 
ance, yet feel certain that sooner or later the covers will come off. 
Can some reader, who has had experience in the matter, throw 
out a few hints for the successful mounting of these very beautiful 
objects? Also stating the name and price of some work treating 
on Micro-crystallography generally. O: Bb: 
429.—Stinging Hairs.—Will some kind reader, who has 
successfully mounted the stinging hairs of the common nettle, 
kindly give the modus operandi, naming the medium used, whether 
weak spirit of wine, glycerine, or glycerine jelly. O. B. 
A CALCULATING-MaACcHINE.—One of the most ingenious of 
recent American inventions is a calculating-machine called ‘The 
“Comptometer.” It is the work of a resident of Chicago, and with 
its aid the most complicated mathematical computations can be 
made with great ease, accuracy, and swiftness. The instrument is 
14} in. long, 7} in. wide, 5 in. high, and weighs 8 lb. It can be 
placed upon an ordinary table. It differs from all other machines 
of this character, as it can be worked with a type-writer key- 
board. This machine performs large multiplications in a second 
of time. It was recently tried by the official experts at the Trea- 
sury at Washington. Various examples not previously known to 
the inventor were given to him for the testing of his apparatus as 
well as to experts detailed from the Treasury. The machine 
always surpassed the experts in speed, and was invariably correct. 
The inventor was given an example like the following :—‘‘ Suppose 
you bring £234 from England to New York, where the rate of 
exchange is $4.847%, what is the American value of your money?” 
In one second of time, this marvellous calculating machine 
recorded the correct answer of $1,134,6034. 
