540 Progress in Science. (October, 
and the pith forced out and placed in hollow bamboos, where it swells out to 
its natural bulk, and dries into a compact mass. This pith is cleverly cut by 
a workman, who holds a sharp knife against the side of the cylinder, which 
is then turned round, so that the pith is cut into a broad strip about 4 feet 
long. This is cut into small squares, and sold in packets for different 
purposes. It is supposed that the paper made from the pith is the rice-paper 
which is imported into this country. It cannot be made until the tree has 
attained a considerable bulk, and is too old to produce many shoots such as 
are ‘used in the first process. The tree from which this paper is made is 
particularly abundant in the island of Formosa. It is at first a small 
shrub, but after flowering it throws out several branches, and grows to a 
height of about 25 feet. It is generally cut down before it attains its full 
maturity, because the pith and bark degenerate in the older parts. Several 
large palmate leaves crown the stem. It has been supposed by many botanists 
that there are two or three different species of plants from which the Chinese 
make their paper, and there are apparently several ways of manufacturing it. 
An enamel for copper cooking utensils is made by fusing together 12 parts 
of white fluor-spar, 12 of gypsum, and 1 part borax, dissolving the mass in 
water to a thick paste, which is applied as a paint to copper vessels, and 
when dry, this is rendered adhesive by being thoroughly baked. 
An alloy, composed of 3 parts of tin, 39°5 copper, and 7°5 parts of zinc, is 
very well adapted for joining brass or copper to iron and steel. 
CHEMICAL SCIENCE. 
Mr. A. P. S. Stuart, an American chemist, remarks that everyone who has 
prepared hydrofluoric acid knows that sulphuric acid and fluor-spar form an 
exceedingly hard compound, which it is very difficult to remove from a pla- 
tinum retort. The formation of this hard mass may be prevented by mixing 
with the fluor-spar about an equal weight of gypsum and the proper quantity 
of sulphuric acid. After the expulsion by heat of the hydrofluoric acid, the 
residuum in the retort is found in a pasty condition, easily removed by water. 
M. Puscher recommends that, to coat zinc with iron, the objects should first 
be plunged into a hot solution of 160 grms. of ferrous sulphate and go grms. 
of sal-ammoniac in 2500 c.c. of boiling water. After two minutes’ exposure 
they should be removed and brushed off in water. This has for its objec 
simply the cleansing of the surface. They are again placed in the bath and 
heated, without brushing or washing, until the sal-ammoniac fumes have 
disappeared, then washed, and this operation repeated three or four times. 
A coating of iron will be found formed on the zinc, which takes a fine polish 
when scratch-brushed. 
Prof. Bischof has found that the analysis of a clay gives a distin@ indication 
as to its power of resisting extreme heats, on the ground that the value of a 
refractory clay varies with the proportion of the alumina to the fusible matter, 
and again with that of the alumina to the silica. The more alumina a clay 
contains in proportion to the fusible matter (iron, alkalies, &c.), the more re- 
fractory is it. Silica, on the contrary, augments its fusibility. Except in 
certain determinate cases, the clays containing alumina, silica, and fusible 
matter in equal proportions, have an equal power of resisting fire. If there is 
taken for clays the general formula—mAl,03+nSiO,+RO, the degree of re- 
sistance to fire is measured by the ratio of The higher the value of this 
fraction, the more refractqry the clay. 
In cases where tubes cannot be conne@ed by india-rubber, corks, &c., Mr. 
Karsten makes a gaslight joint by bending the two tubes to be joined ver- 
tically, the lower one capable of sliding within the other. When in this 
position, the open end of the upper or outer tube’ is surrounded by mercury 
retained in acup, through the bottom of which the smaller tube passes. The 
whole apparatus is most easily constructed, and can readily be taken to pieces 
and put together again. 
