26 
THE YOUNG SCIENTIST. 
Nickeling Small Articles. 
Many unsuccessful attempts have been made 
to nickel small articles by boiling, just as pins, 
hooks and eyes, etc., are silvered or tinned. Dr. 
Kayser is said to have succeeded in coating- 
metals with an alloy resembling German silver, 
thus giving them a handsome finish, and making- 
the surface more durable and permanent than 
that of tin or silver. He first melts together 1 
part copper and 5 parts pure tin— preferably the 
Australian, which has recently come into com- 
merce, almost absolutely pure, yet cheaper than 
Banca tin. The alloy is granulated as usual, 
but not too fine, and then mixed with water and 
tartar, as free from lime as possible, into paste. 
To each 200 parts of the granulated alloy is 
added 1 part ig-nited oxide of nickel, and the 
articles are laid in it. After boiling- a short 
time they become beautifully silvered. Souk? 
fresh oxide of nickel must, of course, be added 
from time to time. Brass and copper articles 
can easily be silvered in this manner without 
previous preparation ; those of iron must first 
be copper plated. By adding some carbonate 
of nickel to the above bath, or to a conmion 
white bath, and boiling-, a coating richer in 
nickel is obtained, and darker, varying in color 
from that of platinum to a blue black, according 
to the amount of nickel salt added. 
saturate the gypsum. These objects are not to 
be cleaned with soap water, since this would 
take up the oleic acid, but should be wiped with 
a cloth, moistened with the acid. The first de- 
scribed method gives the best results, and is 
especially to be recommended in voluminous 
castings.— jD. Ind. Zeitung, ix, 82. 
To Render Plaster Casts Water-Proof. 
Mr. E. Jacobsen gives the following method' 
for prepa 'ng gypsum moulds so that tliey will 
permit being washed. A neutral soap of stearic 
acid and caustic soda is prepared and dissolved 
in about ten times its weight of hot water. The 
moulds or objects are either coated with, or im- 
mersed in this solution. By this procedure the 
color of the object is not affected, it is rendered 
impervious to moisture, and permits the object 
to be washed, even with lukewarm soap watfn", 
since stearate of potassium is only soluble in hot 
water. Soap water is entirely superfluous for 
washing gypsum casts ; warm water is all that is 
requisite. Ordinarily, moulds, etc., are cleaned 
of dust and dirt by means of soap water. This 
removes the dirt, but leaves, in its place, a film of 
soap, which most readily collects and retains 
dust. This same difficulty is presented by gyp- 
sum that has been impregnated with a solution 
of alum and stearine. A coating made with a 
solution of stearate of alumina in benzole be- 
haves in a similar manner. Tho gypsum can 
also be made impormoable to water by satur- 
ating it with a solution of oleic acid in benzine; 
this should be but slightly- colored and oxidized. 
This solution is to be applied to the object when 
cold, and in such quantity as to completely 
Microscopic Lead-Trees. 
A writer in the English Mechanic says : " To 
make the above, place some good-sized pieces i 
of gum arable in a saucer, and then pour in | 
acetate of lead until they are half immersed. 
In about twelve hours some of them will have a 
clear drop of thick gum on the top. Put some \ 
of this on a slide on which zinc has been filed j 
with a fine file, and instantly place over it a 
glass cover. If the slide is at once placed under 
the microscope, the trees may be seen growing, 
but slides that are intended for tlie box should 
be kept under pressure until dry. They will not 
require cementing or papering, the gum being 
quite sufficient for the purpose. I discovered 
this method about ten years since, and find the 
slides I then made to be in perfect preservation. 
The finer the zinc particles and the weaker the 
acetate solution, the finer will be the trees, and 
vice versa." 
Patina on Zinc. 
Patina is a term applied to the coating which 
the natural corrosion of the elements produce 
on metals. A solution of molybdic acid or of 
molybdate of ammonia in weak aqua-regia, or 
a solution of molybdic acid in an excess of 
strongly diluted soda lye, furnishes, according 
to M. de Kletzinsky, a very good bath with 
which to obtain a patina on objects cast in zinc. 
The objects are simply immersed in a bath, 
when they shortly acquire a brownish patina, 
very agreeable to the sight, and having a charac- 
teristic iridescence. The effect here described 
is due to the formation of a thin film of oxide of 
molybdenum, which develops the colors of po- 
larization, and which adheres strongl\' to the 
zinc. 
Crystallized Wood and Paper. 
According to Professor Boettger, the simplest 
method of giving paper and wood surfaces a 
crystalline coating is as follows: Mix a very 
concentrated cold solution of salt with dextrine, 
and lay the thinnest possible coating of the 
fluid on thf^ surface to be covered, by means of 
a broad soft brush. After drying, the surface, 
has a beautiful bright mother-of-pearl coating, 
which, in consequence of the dextrine, adheres 
firmly to paper and wood. The coating maybe 
