520 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



tions from it, and this is best done by cylindrical surfaces. 

 Plain arches are the worst form ; flat ceilings are better, but 

 far less effective than those that are indented or broken up 

 by ornaments in relief; pointed arches, as in Gothic architect- 

 ure, are less effective. 



7. The walls are very frequently the cause of more dis- 

 turbance than the ceilings; and, since these can seldom be 

 built purely with reference to acoustic proj^erties, it becomes 

 necessary to ameliorate, as far as possible, the ill effects re- 

 sulting from the adoj^ted constructions. The portion of the 

 walls above the plane of the speaker is of less importance ; 

 most attention should be bestowed on the zone between the 

 level of the speaker and the hearer. This zone should be 

 broken up by relief and profile ornamentations, etc., and by 

 niches of small diameter. Casettes are to be avoided, as also 

 plain surfaces on the pillars. 



8. The material of which the surfaces should be made is 

 still undecided. Wood, metal, or stone has each its disad- 

 vantage. The surfaces should probably be constructed to 

 act as little as possible like sounding-boards; that is to say, 

 the more important point to which attention should be given 

 is the method of supporting the board or plaster, if these be 

 introduced instead of stone or brick. Viert. Deutsche Poly- 

 tech. Verein, 1872,187. 



EXPERIMENTS ON STEAM-BOILER EXPLOSIONS. 



Among other enactments by Congress, is one authorizing 

 the President to cause such experiments to be made and such 

 information to be collected as in his opinion will be useful 

 and important in preventing the bursting of steam-boilers; 

 and the sum of $100,000 is appropriated for the necessary ex- 

 periments. Acts of Con(/7'ess, JVb. 80. 



GLYCERINE AS AN ANTI-INCRUSTATOR IN STEAM-BOILER&. 



According to the Journal of the Franklin Institute^ g^ycer 

 ine is highly recommended as an anti-incrustator in steam- 

 boilers. The effect of this addition is to increase the solubility 

 of the lime salts, and to form with them a soluble compound. 

 When the lime salts accumulate to such an extent as to be 

 no longer soluble by glycerine, they are deposited in the 

 form of a gelatinous sediment, which does not adhere to the 



