Laminated poles and pole tips are coming into increased use, and this, says "Power," is a feature of modern dynamo and alternator construction. For traction dynamos this construction is found to be of advantage, because the magnetism more quickly responds to changes of load. It is obviously of little avail to fit the engine with an elaborate cut-off and governing gear if the magnetism of the dynamo is sluggish. In the case of alternators, and to a certain extent of dynamos, lamination is of advantage is reducing eddy currents. Further, the designer is dealing with material which can be depended on to come up to a certain magnetic value. Unfortunately this is not the case with cast steel or cast iron. When the complete pole is laminated, the block is often cast into the yoke. This method, though cheap, is not bo good as bolting on the poles, because the plates must be affected by the heat and can be insulated only with oxide. The molten metal would destroy paper or japan. For dynamos, pole shoes are usual, so as not to have the air-gap area too concentrated. The shoe also acts as a support to the magnetic coil.
The largest raindrops are about one-fifth of an inch in diameter. Their size has been determined by allowing rain to fall into a thick layer of flour, each drop forming a pellet of dough, and these pellets are compared with dough pellets obtained, it is said, from drops of known size delivered upon the flour by artificial means.
The freezing system of tunneling is to be adopted in the construction of the new tube railroad for Paris at the point where the track will pass beneath the Orleans trunk railway. For various reasons, the ordinary shield system will not be suitable. The earth is to be frozen to a temperature of 30° below zero, so that the excavators can cut the tunnel without incurring any danger of collapse before the metal lining has been placed in position. The workmen, however, will experience some inconvenience while working at such a low temperature, but it is thought that this method offers the only solution of the problem.
Vast quantities of chalk are annually made into tooth powders. It is the base of most of the dentri-fices. Mixed with the chalk as detergents are charcoal, cuttlefish bone and pumice. Bleaching salts and various acids also constitute parts of some dentrifices and constitute a grave danger to the teeth.
Phosphor bronze is an alloy of phosphor, tin and copper, containing usually 6.053 to 0.76 per cent phosphorus and four to ten per cent tin, balance copper. It is as tough as wrought iron, more ductile than copper and is capable of withstanding great wear.
The waste heat from a boiler furnace that escapes through the chimney is considerable, and to some extent unavoidable, for if all the heat were utilized, the chimney would not draw, since it is the heat in the chimney which first produces the draught in the furnace necessary for burning the fuel. Nevertheless, too much heat escapes by the chimney in most cases. A method recently patented professes to rectify this defect by bringing the flue containing the products of combustion to the place where the steam is applied before it passes into the chimney. The air, steam or hot-water and feed-pipes are passed through this flue, so that the heat contained in the gases of combustion prevents radiation from the pipe in question and contributes to the heating of the air, water and steam.
Polished aluminum has a slightly bluish tint like tin, but this can be improved. In polishing aluminum the grease is removed with pumice stone, and then is used an emery paste mixed with tallow, forming cakes which are rubbed on the polishing brushes. Finally, red polishing stuff, moistened with oil of turpentine, is used.