oxide also, and the drawing be thereby
spoiled.

But the most certain material to be used is the hyposulphite of soda.
One ounce of this salt should be dissolved in about a pint of distilled
water. Having previously washed the drawing in a little lukewarm
water, which of itself removes a large portion of the muriate of silver
which is to be got rid of, it should be dipped once or twice in the
hyposulphite solution. By this operation the muriate which lies upon
the lighter parts will become so altered in its nature as to be
unchanged by light, while the rest remains dark as before.

It will be evident from the nature of the process, that the lights and
shadows of an object are reversed. That which is originally opaque
will intercept the light, and consequently those parts of the
photogenic paper will be least influenced by light, while any part of
the object which is transparent, by admitting the light through it,
will suffer the effect to be greater or less in exact proportion to its
degree of transparency. The object wholly intercepting the light will
show a white impression; in selecting, for example, a butterfly for an
object, the insect, being more or less transparent, leaves a
proportionate gradation of light and shade, the most opaque parts
showing the whitest. It may be said, therefore, that this is not
natural, and in order to obtain a true picture--or, as it is termed, a
positive picture--we must place our first acquired photograph upon a
second piece of photogenic paper. Before we do this, however, we must
render our photograph transparent, otherwise the opacity of the paper
will mar our efforts.

To accomplish this object, the back of the paper containing the
negative, or first acquired photograph, should be covered with white or
virgin wax. This may be done by scraping the wax upon the paper, and
then, after placing it between two other pieces of paper, passing a
heated iron over it. The picture, being thus rendered transparent,
should now be applied to a second piece of photogenic paper, and
exposed, in the manner before directed, either to diffused day-light or
to the direct rays of the sun. The light will now penetrate the white
parts, and the second photograph be the reverse of the first, or a true
picture of the original.

Instead of wax, boiled linseed oil--it must be the best and most
transparent kind--may be used. The back of the negative photograph
should be smeared with the oil, and