A waterproof cement has been patented in Germany. A mixture of vegetable wax and caustic lime, in boiling water, is added to unground Portland cement clinker, and all ground together. The inventor makes the claim that one-half-inch coating of this cement placed on a brick wall will render it absolutely waterproof. The formula is given as follows; To each 200 lbs. of cement clinker is added a mixture of three-fourthspound of Japan vegetable or berry wax, and one ounce of caustic lime, which has been dissolved in fourteen pints of boiling water. These ingredients are thoroughly mixed and, when cooled, are dried and ground very fine with cement clinker.

The " Mechanical World" recently contained an epi" tome of a lecture by A. B. Roxburgh, of the National Gas Engine Company, Ltd., in which it was stated that about one-fourth of all the gas made in Great Britain is employed in driving gas engines. The lecturer estimated that in the United Kingdem alone there are manufactured at least 200 gas engines per week. Averaging them at the very low size of ten brake horsepower each would give a weekly production of 2000 horse power. It was deemed likely, however, that the actual amount is double that figure.

In Cuba alcohol is produced and sold from 12 to 15 cents a gallon, and it is said to make an excellent fuel for running engines. It produces no soot or disagre-able odors. When the law recently passed by Congress to denaturize alcohol in the United States becomes operative, it is expected greatly to increase the use of the article both for fuel and other purposes.

Uranium is a remarkably heavy metal having the high specific gravity of 18.6. It was discovered in 1789 by a German chemist in the mineral uraninite or pitchblende. Uranium is contained in uraninite gumnite, a hydrated calcium lead uranium silicate, torbenite, a, hydrated copper uranium phosphate. The metal is prepared by heating a mixture of uranium chloride, sodium chloride and carbon or of uranium chloride, sodium chloride and metallic sodium. It is a white metal resembling nickel.

The practice of hardening steel dates back to the remotest antiquity. Homer, Pliny and Lucretius refer to the hardness imparted to iron taken from the forge and plunged in water. The ancient Egyptians heated meteoric iron in the forge at a temperature somewhat below the melting point, until it had absorbed enough carbon from the fuel to give it the requisite hardening properties, and then fashioned their weapons and tools from the metal thus obtained.

The units of weights and measures in the United are practically those used in the colonies prior to the formation of our government. While Congress has never definitely authorized the weights and measures in common use, it has sanctioned their use by its act of June 14. 1836, providing that accurate copies of the yard, pound, etc., be furnished as standards to each state.

The volumometer is an instrument for determining the specific gravity of solids by measuring the amount of water or other liquid displaced by it. A simple form is a flask having a long narrow neck and an opening at the side through which the solid may be introduced, the neck being graduated from the bottom upward. T!ie flask is filled to the zero mark with some fluid in which the solid is not soluble; on turning it on its side the stopper is removed and solid introduced. When turned back to an upright posture again the liquid is forced up the stem and the volume reading is the amount of liquid displaced by the solid. From this the specific gravity is easily obtained.

The lifetime of a good watch is 50 years. In its daily duties the balance vibrates 18,000 times every hour, 432,000 time a day, or 157,680,000 times a year. The hair spring makes a similar number of vibrations and an equal number of ticks from the escapement. If it is a really good watch, multiply 157,680,000 by 50, which gives 7,884,000,000 pulsations for 50 years. The chances are that the watch may even then be in serviceable condition. This is a marvellous record, considering the small quantity of food that has been consumed by its constant action. We say food because whatever labors must be fed, and the watch "lives" on about 16 inches of mainspring every 24 hours, which furnishes the power.

In paints the most permanent of blues is ultra marine, while Prussian blue and indigo are liable to fade. Cobalt, however, is the most lasting of all blues. Among the reds the only really unchanging colors are vermiliou and the ochres; madders, carmines and crimson lakes are likely to fade, the latter two quite rapidly. Oxide of chromium is a permanent green. The staple yellows are Naples yellow, cadmium, raw sienna and yellow ochre. In brown, raw and burnt umber retain their tint, forever.

Water gas is a mixture of gases produced by the action of steam on incandescent carbon. The carbon first decomposes the steam, forming hydrogen and carbon dioxide and the latter gas then combines with more carbon to form the inflammable carbon monoxide. Thus water gas is mainly a mixture of hydrogen and carbon monoxide. Pure water gas is non-luminous, but it is rendered luminous, by mixing with various gases obtained from petroleum, the luminous material being known as carburetted water gas.

It is stated in Washington on good authority that the War Department will probably buy several automobile ambulances. A car of this type was recently purchased from a company, and has been subjected to trials by the medical department of the army. The officers have pronounced the ambulance of great value although they are of the opinion that some changes in the arrangement and equipment of the vehicles should be made. It is understood that these ambulances will be used in the field in case of war, and will be attached to every brigade hospital. One of the principal advantages of these vehicles is their speed and the fact that they do not require horses. The medical officers who have been examining the motor ambulances say that there will be no great difficulty in making the required changes in the ambulances.