112 
THE YOUNG SCIENTIST. 
renders India ink, whicb always contains a little 
gelatine, indelible. Reisenbichler, tbe discoverer, 
calls this kind of ink " Harttuscb," or "bard 
India ink;" it is made by adding to the common 
article, when making, about one per cent, in a very 
fine powder, of bichromate of potash. This must 
be mixed with the ink in a dry state; otherwise, it is 
said, the ink could not be ground up easily in 
water. Those who cannot provide themselves 
with ink prepared as above in the cake, can use a 
dilute solution of bichromate of potash in rubbing 
up the ink; it answers the same purpose, though 
the ink should be used thick, so that the yellow 
salt will not spread. 
Hatching Alligator Eggs.— The New York 
Aquarium has received from Florida a large num- 
ber of alligators' eggs, and has made arrangements 
to hatch them artificially. This will prove an inter- 
esting and instructive experiment. It is expected 
that a young alligator will emerge from its shell 
every hour during the day, affording every visitor 
a chance to see the curious sight. Tnis experi- 
ment will be the first of the kind ever tried, and 
should it prove successful, will be of considerable 
scientific importance. The attempt to keep Cali- 
fornia salmon alive during the hot weather has 
been successful. Heretofore these invaluable fish 
have invariably died during the summer months. 
At the Aquarium one of the tanks has been turned 
into a refrigerator, and these fish are now perfectly 
healthy. 
EXCHANGES. 
In this column yearly subscribers who may wish 
to exchange tools, apparatus, books, or the pro- 
ducts of their skill, can state what they have to 
oflfer and what they want, wUhotU charge. Buying 
and selling must, of course, be carried on in the 
advertising columns. 
Wanted, a 5 by 8 stereoscopic camera 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. 8. Price, King's 
Eiver, Cal. 
Wanted, in exchange for books, a second-hand 
aquarium. Address P. O. Box 124, Bridgeton, 
N. J. 
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, cost $8, for a music box of same price, in 
good order. L. D. Snook, Barrington, Yates Co., 
N. Y. 
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 Ist and 2d 
Readers Standard Phonography; tools or advanced 
scientific books preferred in exchange, E. H. Bid- 
well, Vineland, N. J. 
Magic lantern, nine slides (two mechanical) in 
complete order, in exchange for good compound 
microscope. T. R. Barwood, Fiatbush, L. I. 
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, 1,212 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, hooka 
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, Fiatbush, 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. 
A set of chemicals and apparatus; also a set of 
wood engraver's tools, glass and instruction book, 
to exchange for a scroll saw and a microscope. The 
chemicals and tools cost nearly $40; will give a good 
trade. F. H. Jackson, Angelica, N. Y. 
Wanted, a copy of Holtzapfers " Mechanical 
Manipulation." State what is wanted in exchange. 
E. W., Box 4875, New York. 
Wanted, a small turning lathe in exchange for a 
pair of telephones. J. C, care Young Scientist. 
Scroll saw wanted in exchange for handsome 
portfolio of six water color sketches. Address 
F. S., care Box 4875, New York. 
Specimens of the marbles, granites and minerals 
of Vermont, in exchange for Western minerals, or 
good fossils; minerals and fossil woods from the far 
West specially desired. Dr. H. A. Cutting, State 
Geologist, Lunenburgh, Essex County, Vt. 
Wanted, complete Lester combination scroll saw 
in good condition; books in exchange. J.T.Jack- 
son, Box 48, Metuchen, N. J. 
Gold watch (cost $150) in exchange for a good 
microscope. E. W., Box 4875, New York. 
Wanted, microscope, or scientific and mechanical 
books and apparatus, in exchange for printing 
press, cost $21, with or without type and material. 
J. P. Burbank, Salem, Mass. 
Cigar machine to exchange for bracket saw or 
good microscope. Leonard Alexander, Linneus, Me. 
Wanted, microscope ; new Tillotson relay and 
part cash given in exchange. W. O. F,, 83 Down- 
ing street, Brooklyn. 
To exchange, a Kidder electric battery, for a pri- 
vate line telegraph instrument. Charles L. Feld- 
kamp, 200 W. Randolph street, Chicago, Ills. 
Camera for taking portraits wanted; state what 
is wanted in exchange. J. F. H., care o: this jour- 
nal. 
