May 



[889.] 



SCIENCE. 



335 



the air is generally conveyed through flues built into the interior 

 walls ; the volume and rate of discharge being governed by the 

 register through which the air escapes. 



The object always is to discharge the air either at or towards 

 the cold outer wall, but it must be admitted that it takes a great 

 deal of experience in this line to enable any one to lay out a perfect 

 working system. 



This system, known as the " blower system," possesses many 

 advantages. Above all, it is positive. The air, being forced into 

 the building, must of necessity thoroughly circulate through it, 

 creating perfect distribution of heat, and ample ventilation. The 

 source of supply of the air introduced being always under control, 

 there can be no opportunity for the presence of injurious impurities. 

 In any system dependent upon natural agencies to produce venti- 



lation, changes in the weather always have a serious, and in some 

 cases a perfectly nullifying effect. With mechanical ventilation, 

 this can never occur, for the pressure produced by the fan is far 

 in excess of that due to any changes in the atmosphere. 



In the blower system, a marked saving is made in the amount of 

 heating-surface required. The large amount of air passing through 

 the heater causes such a rapid condensation of steam, that each 

 square foot condenses from three to five times as much steam as 

 will be condensed by the same area in an ordinary coil-radiator ; in 

 other words, only one-third to one-fifth the pipe is required to do 



the same amount of heating. The saving in the heating-surface 

 will usually pay for the fan and engine, so that the system becomes 

 no more expensive than a direct-heating system. 



But while in a direct system there is always danger from fire, 

 freezing, and leakage, this is all obviated in the blower sys- 

 tem. All the pipe is combined in a single heater, incased in a fire- 

 proof jacket, and all valves are within easy reach, placing the en- 

 tire control of the apparatus in the hands of a single individual. 

 Furthermore, a much more rapid change in the temperature of the 

 building is possible with the blower system than with any other 

 system, either direct or indirect. 



Most assuredly the system is worthy of investigation by any one 

 requiring either heat or ventilation. It is now in use in some of 

 the largest manufactories in the country, such as the Pacific Mills, 

 Lawrence, Mass.; the New O. N. T. Clark Thread Mill at Kear- 

 ney, N.J.; the Morgan Engineering Company, Alliance, O.; Niles 

 Tool Works, Hamilton, O., etc. 



Mr. Sturtevant has recently issued a handsome eighty-page il- 

 lustrated treatise on ventilation and heating, which we are informed 

 will be sent to any one requesting it. 



BRICK FOR STREET-PAVING. 



There are perhaps fifty cities in the United States using brick 

 pavements. Some have had them over fifteen years. In Decatur, 

 111., brick pavements have been in use for six years ; in Blooming- 

 ton they have been used for fifteen years ; and in Charleston, 

 W.Va., for a longer time. They are in use in Jacksonville, Peoria, 

 Quincy, and Springfield, 111., also in Kansas and Nebraska ; and a 

 number of cities in Ohio are using them with good results. 



All brick pavements have not given satisfaction, as the contrary 

 effect has been produced when common building-brick has been 

 used. They begin to show the effects of wear in a very short time 

 if soft brick is used, but good hard brick gives satisfaction. There 

 is no paving-material equal to hard brick, excepting granite blocks, 

 and it is doubtful if they would last as long were they as small as 

 bricks. There are few cities in the United States where brick 

 could not be laid for one-third the cost of granite blocks. 



It may be urged that suitable clay for manufacturing paving- 

 brick is scarce, but there is nothing in this country so plentiful. 

 Of over twenty different samples of clay sent from various portions 

 of Illinois and other States to the Decatur Tile Company, all ex- 

 cepting one have been made into paving-brick, although some kinds 

 are much better for the purpose than others. This company has 

 made about five million bricks per year during the past four years, 

 seventy-five per cent being paving-brick. Over five miles of the 

 streets of Decatur are paved with brick, and the City Council is 

 planning to have more of them thus paved. 



The clay used by the tile company mentioned is a common yel- 

 low joint clay, having a large percentage of silicate and iron. It is 

 tempered or soaked for twenty-four hours before using, then carried 

 by a belt to a stone-separator and crushers. Dropping from the 

 crushers to an elevator, it is fed to the brick-machine. From this 

 machine it runs in three streams upon a moving table, and is cut 

 by wires, fastened in a frame, into bricks eight and a half inches in 

 length. The die through which the clay is pressed on leaving the 

 machine is 4 by 2| inches. The bricks are then set upon drj'ing- 

 cars to be dried in hot-air tunnels, or set on slats in a building 

 warmed by steam, or placed on a drying-floor heated from the 

 burning kilns or small furnaces. When dry, they are carried in 

 wheel-barrows and set "skintling," or at angles across each other, 

 to allow the heat to pass between them in the down-draught kilns. 

 Experience has proved that good paving-brick cannot be burned in 

 open, up-draught kilns, if made from the clay described. 



While some kinds of clay will stand fire long enough to burn as 

 hard as rock in open kilns, yet even then the bricks would be much 

 better in shape and quality if burned in closed kilns. The bricks 

 are burned from six to seven days, the first three or four days very 

 slowly, called "water smoking." It is necessary to watch very 

 closely when finishing the burning, as there is great danger of run- 

 ning the bricks together and spoiling the whole mass. 



The great drawback to using all kinds of clay is owing to the 



