Popular Science Monthly 



303 



Straightening Warped Boards 



WARI'KI) hoards may bo straight- 

 ened by the following method and 

 they will stay' straight. Resaw the 

 l)oard into strips, about 3 ins. wide. 

 Joint all edges and glue the pieces 

 together, being careful to reverse e\x'ry 

 other piece sidewise. Then plane the 

 surface carcfidl>' and the board will not 

 warp again. — L. G. Abele. 



Sloping a Drawing- Board 



An adjustable 

 sloping drawing- 

 board 



THERE is many a mechanic who 

 finds that if his drawing-board 

 were only sloped he could work much 

 better. 



The accompanying drawing will ex- 

 plain itself. A block of wood ha\ing 

 three or four headless pins driven in the 

 edge will hold the drawing board, the 

 slope being regulated by the position of 

 the block. — Alfred R. \V.\r.sTAFF. 



Keeping Food Without Ice 



FOR the temporary' preservation of 

 such food products as rapidly spoil 

 by heat, a modification of the Mexican 

 "011a" is used with success. The "Olla" 

 is a water jar of porous, unglazed native 

 biscuit work, which has the projjerty of 

 keeping the contained water cool, even 

 in the severe temperatures of the 

 southwestern deserts, when filled and 

 hung in a current of air. Hanging in 

 the sun keeps it cooler. The principle 

 invoK't'd is the reduction of temperature 

 due to rapid evaporation, the water 

 which penetrates the clay being rapidly 

 evaporated from the surface of the jar, 

 lowering the temperature of its contents. 

 This principle is applied by dwellers 

 far from an ice supply, as follows: 



A frame of rec|uired size is made fnjin 

 a wood with no decided taste or oilor. 

 The "cucumber" wood, from which the 

 old-fashioned pump-logs were fashioned, 

 is probably the best. Bass or linden is 

 also used. This frame is cov'ered with 

 copper wire screen cloth, using turned 

 copper tacks for fastenings. This again 

 is covered with two or three thicknesses 

 of cheese-cloth, stretched and tacked. 

 A tin gutter is ,so made that a properly 

 designed slot in the bottom may be 

 filled with cotton lamp-wicking, which 

 projects in such manner as to touch the 

 cheese-cloth enclosure, to which it is 

 stitched at intervals to insure positive 

 contact. The floor of this arrangement 

 is elevated in such a way as to permit 

 any excess of moisture reaching the 

 cheese-cloth to drip off and run away 

 to waste. By means of a regulating 

 valve the water supply admitted to 

 the upper gutter is just sufficient to 

 keep the cheese-cloth constantly damp. 

 The entire apparatus should be located 

 in a cool passage or a shady porch. In 

 either case a free circulation of air is 

 essential. The evaporation reduces the 

 temperature inside the device to a 

 noticeable degree . 



If a pressure source of water supply is 

 available, it may be used. If not, a 

 bucket can be provided with a prf)per 

 faucet, and furnish the water supply. 

 A collapsible modification of the "Olla" 

 carried by a picnic party will replace the 

 thermos bottle as a means of keeping 

 the liquid refreshments cool. 





Constant evaporation of water from a strip 



of cheese-clotli keeps the interior of the 



box cool in the hottest weather 



