270 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



ally cooling and descending would reach the uppermost 

 ranges of shelves first in their descent, is made quite under- 

 standable. He asserts that he lias found in the leather bind- 

 ings of certain old library books that had become quite brit- 

 tle as much as eight per cent, of sulphuric acid. Late re- 

 searches on the permeability to gases and vapors of various 

 materials used for building purposes have demonstrated that 

 when not saturated with moisture, bricks, sandstone, tufa, 

 mortar, and cements are permeable; while granite, porphyry, 

 slate, alabaster, and limestone are practically impermeable. 

 The sanitary bearing of these observations is obvious. 



Muter has proposed a method of detecting the addition 

 of glycerin to milk for the purpose of maintaining its nor- 

 mal specific gravity when it is watered. The residue after 

 evaporation is treated with a mixture of alcohol and ether, 

 and the residue of the evaporation of these solvents is exam- 

 ined for glycerin. If found, its amount must be determined 

 by making a complete analysis of the milk. 



Peckham has investigated the cause of the explosion of 

 the flour-mills in Minneapolis in May last, and gives it as his 

 opinion that the explosion was due to the ignition of the fine 

 dust of flour, with which the mill was filled, by sparks coin- 

 ing from millstones which had been allowed to run dry. In 

 the dust-house connected with these stones several hundred 

 pounds of dust a day settled under ordinary circumstances. 



A correspondent of Nature writes from Burton-on-Trent 

 that explosions during the grinding of malt, due to the igni- 

 tion of the fine dust in the air, are not uncommon. Any fine 

 impalpable powder, such as flour, sugar, coal-dust, wood- 

 dust, may be thus the cause of serious explosions. 



Clemandot has patented in England a process for produc- 

 ing the beautiful iridescence on glass which has lately at- 

 tracted attention. The glass is simply treated, under press- 

 ure and at a temperature of 120 to 150, with a ten to 

 twenty per cent, solution of hydrochloric acid. The colors 

 are produced by interference. 



Silliman has invented a process for making Britannia met- 

 al articles sonorous by heating them for fifteen or twenty 

 seconds to 5 below the melting-point in a paraffin bath. 



