The extreme solubility of this salt is too well-known, as is also the cold produced when it is dissolved: one pound dissolved in two of boiling water will give a solution that is merely lukewarm, the surplus heat being absorbed during the dissolution of the crystals. This is merely an example of a law of wide applicability that a solid substance when converted into a liquid absorbs heat. The converse of this law - also of wide applicability - that when a liquid is converted into a solid it disengages heat, is less familiar. The experiment we refer to is an illustration of this law. A perfectly clean glass flask is taken - size is unimportant - and about half filled with clean crystals of hypo; they must be quite free from bits of wood or other extraneous particles. It is then held over a gas flame until the crystals liquefy - hypo will always dissolve in its own water of crystallization. A plug of cotton is placed in the neck of the flask, first making sure there is no suspended matter in the newly formed liquid. If then put gently away in a cupboard it will be found to retain its liquid condition for weeks, or even months, if left undisturbed. When it is desired to make the experiment the flask is taken gently from its resting place, and first putting it on the palm of the hand, cart-fully removing the plug, a tiny crystal of hypo is dropped into the liquid. In a second or two this crystal sets up the crystallization of all the fluid, which in a brief time becomes solid and becomes so hot that the flask cannot be held in the hand, a remarkable illustration of heat being evolved when a liquid becomes solid.

From An Artura Iris Print Home Portrait By Philip Conklin.

From An Artura Iris Print Home Portrait By Philip Conklin.

Clean Graduates

The best definition of "dirt" is "matter in the wrong place" and there are few things more important to a photographer than to keep his graduates clean. The extra time taken in thoroughly rinsing the graduate after use and hanging it up to drain on a peg will be well repaid in the saving you will effect of both time and material.

From An Artura Iris Print By Philip Conklin Troy, N. Y.

From An Artura Iris Print By Philip Conklin Troy, N. Y.

From An Artura Iris Print By Philip Conklin Troy, N. Y.

From An Artura Iris Print By Philip Conklin Troy, N. Y.