136 
THE YOUNG SCIENTIST. 
Inquiries. 
38. What is the composition used for making 
electrotype moulds? How are the moulds taken 
from the type? A. W. P. 
89. Can any of your readers furnish directions 
for dissecting the abdomen and internal organs of 
the spider? Taylor, formerly State Entomologist 
of Georgia, speaks of a mould being taken by drop- 
ping melted suet therein, but does not give pro- 
cess. Entomologist. 
Answers. 
40. In answer toB. G. P. (36), the acid used in 
engraving upon steel is nitric (poison). The best 
method of applying it is as follows: Clean the part 
to be engraved upon, then pour over this a thin 
layer of melted wax; allow it to harden, and scratch 
on the wax the name or device with a pin, so that 
wherever the pin has been the surface of the object 
to be engraved is free from wax; now with a little 
stick, bruised so as to look like a little brush, apply 
the acid over the wax, allowing it to eat the iron 
or steel in the lines made by the wax; ten minutes 
will be sufficient to engrave the work; then wash 
and remove the wax. J. 0. 
41. In answer to B. G. P. (36), first clean the 
blade of the knife thoroughly, and then apply a 
coating of beeswax to the blade, being careful to 
get the whole surface covered. Then cut the name 
in the wax, being careful to remove the wax from 
the blade wherever the etching is required, after 
which apply strong muriatic acid for a few seconds, 
and then wash thoroughly in water. Subsgribeb. 
EXCHANGES. 
In this column yearly subscribers who may wish 
to exchange tools, apparatus, books, or the pro- 
ducts of their skiU, can state what they have to 
offer and what they want, withoiU charge. Buying 
and selling must, of course, be carried on in the 
advertising columns. 
Hamilton, Up. Held, and Carboniferous fossils; 
also eastern minerals, to exchange for fossils, min- 
erals, shells, or Indian relics; hst of duplicates and 
desiderata sent upon application. B. H. Wright, 
Penn Yan, N. Y. 
To exchange, 2-column adding machine, Amer- 
ican Manual of Phonography, collection of foreign 
stamps and Confed. money, books, and files of 
illustrated and literary papers, for printing mate- 
rial or press; or for spy or opera glass. J. N. Hus- 
ton, Box 108, Chase City, Va. 
Minerals, fossils, Indian relics, shells, woods, 
fossil woods, skulls, etc., to exchange for type, sea 
shells, fossils , foreign coi n s and stamps . Frank M. 
Farrell, Box 37, Cobden, 111. 
Great variety of good wood cuts to exchange for 
good compound microscope, in good condition, of 
at least 200 diameters. Austin Cravath, White- 
water, Wis. 
Bohn's first lessons on Geology, Mineralogy and 
Possil Botany, and pair of American Club Skates, 
given in exchange for a German silver fife and in- 
struction book. Thos. F. Sheridan, Bridgeport, Ct. 
Gold watch (cost $150) in exchange for a good 
microscope. E. W., Box 4875, New York. 
Asmall steam engine in good order, cost $1.50, 
for a dark (bulls-eye) lantern. Geo. H. Umbach, 
139 Ross street, Brooklyn, N. Y. 
Wanted, a set of wood engravers tools; Spencer's 
Psychology, two volumes, given in exchange; also 
other books for exchange. T. S. Price, Slack's 
Canon, Monterey Co., Cal. 
Wanted, small turning lathe about IJ by 12 ins.; 
state what is wanted in exchange. D. Abrahams, 
195 East Broadway, New York. 
Wanted, back numbers of the "American Natur- 
alist;" will give "Harper's" or "Scribner's" 
monthly. Hulbert, 131 West Fifty- third street. 
New York. 
Wanted, a 5 by 8 stereoscopic camtjra box; Fleet- 
wood scroll saw, nearly new in exchange. L. L. 
Roberts, 1,203 Arch street, Philadelphia, Pa. 
Wanted, good microscope and Vols. I and II of 
"American Journal of Microscopy, or thorough 
works on botany; thorough instruction in short- 
hand, by mail, in exchange. T. S. Price, King's 
River, Cal. 
A collection of postage stamps for small cannon 
or small printing press; will pay difference. C. L. 
Hackett, lock box 2,210, Roanoke, Ind. 
To exchange a good magic lantern, painted 
slides, cose $8, for a music box of same price, in 
good order. L. D. Snook, Barrington, Yates Co., 
McAllister's Household microscope and American 
Agriculturist microscope, for small 5 or 6 inch turn- 
ing lathe, or offers. J. Frank Weaver, Brooklyn, 
Conn. 
Graham's Handbook, Synopsis, and 1st and 2d 
Readers Standard Phonography; tools or advanced 
scientific books preferred in exchange. E. H. Bid- 
well, Vineland, N. J. 
Complete outfit for stamping key checks, worth 
$10, in exchange for practical receipt books, or 
bracket saw with lathe and drill attachment. John 
Whitty, Jr., Polloksville, N. C. 
Woodward's Hospital Microscope wanted in ex- 
change for chemical scales and weights; difference 
in cash. J. Siler, 1,242 Broadway, St. Louis, Mo, 
For exchange, an entire printing outfit, cost $50; 
state what you have to exchange. F. R. Miller, 
750 East Fourth street. South Boston, Mass. 
Good $50 job printing press, in perfect order, for 
a scroll and circular saw, or scroll saw alone; saw 
must be in good order. Samuel J. Jones, Box 137, 
Oxford, N. C. 
Wanted, foot power scroll saw, lathe, or both 
combined, or good microscope, for minerals, books 
on plant culture. Art Journal in parts, or cancelled 
postage and revenue stamps, D. S, Kimball, 48 
Exchange Place, New York. 
Wanted, small steam engine and boiler of from 
1 to 2 horse-power; state what is wanted in ex- 
change. Address Jno. McElvery, Flatbush, L. I. 
Wanted, telegraphic and mathematical instru- 
ments; Pitman's Phonography in exchange; also 
thorough instruction in same by mail. F. S. P., 
King's River, Fresno County, Cal. 
Wanted, a copy of Holtzapfel's "Mechanical 
Manipulation." State what is wanted in exchange. 
E. W., Box 4875, New York. 
Specimens of the marbles, granites and minerals 
of Vermont, in exchange for Western minerals, or 
good ff ssils; minerals and fossil woods from the far 
West specially desired. Dr. H. A. Cutting, State 
Geologist, Lunenburgh, Essex County, Vt. 
