Method of making Artificial Whetstones.—­Gelatine of good quality is dissolved in its own weight of water, the operation being conducted in a dark room.  To the solution one and a half per cent. of bichromate of potash is added, which has previously been dissolved in a little water.  A quantity of very fine emery, equal to nine times the weight of the gelatine, is [Transcriber’s Note:  The original text reads ‘itimately’] intimately mixed with the gelatine solution.  Pulverized flint may be substituted for emery.  The mass is molded into any desired shape, and is then consolidated by heavy pressure.  It is dried by exposure to strong sunlight for several hours.

How to Toughen Paper.—­A plan for rendering paper as tough as wood or leather has been recently introduced; it consists in mixing chloride of zinc with the pulp in the course of manufacture.  It has been found that the greater the degree of concentration of the zinc solution, the greater will be the toughness of the paper.  It can be used for making boxes and for roofing.

How to Mend a Broken File.—­There is no tool so easily broken as the file that the machinist has to work with, and is about the first thing that snaps when a kit of tools gets upset upon the cross-beam of a machine or a tool board from the bed of an engine lathe.  It cannot even be passed from one workman to another without being broken, if the file is a new one or still good for anything, if an apprentice has got anything to do with it, and they are never worth mending, however great may be their first cost, unless the plaster of Paris and lime treatment can make a perfect weld without injuring the steel or disturbing the form of the teeth.  Steel that is left as hard as a file is very brittle, and soft solder can hold as much on a steady pull if it has a new surface to work from.  Take a file, as soon as it is broken, and wet the break with zinc dissolved in muriatic acid, and then tin over with the soldering iron.  This must be done immediately as soon as the file is broken, as the break begins to oxydize when exposed to the air.  And in an hour or two will gather sufficient to make it impossible for the parts to adhere.  Heat the file as warm as it will bear without disturbing its temper as soon as well tinned, and press the two pieces firmly together, squeezing out nearly all the solder, and hold in place until the file cools.  This can be done with very little to trim off, and every portion of the break fitting accurately in place.  Bring both pieces in line with each other, and, for a file, it is as strong in one place as in another, and is all that could be asked for under the very best of welding treatment.

What will Fasten Pencil Markings, to Prevent Blurring.—­Immerse paper containing the markings to be preserved in a bath of clear water, then flow or immerse in milk a moment; hang up to dry.  Having often had recourse to this method, in preserving pencil and crayon drawings, I will warrant it a sure cure.