SCIENCE 



[N. S. Vol. XXVIII. No. 724 



furthermore, that it facilitates the opera- 

 tion of the hood vents. The hood vents 

 should, in my opinion, be joined up in a 

 separate system with a separate fan. This 

 fan located in the attic will draw the air 

 out at a pressure of about three times as 

 strong as that of the ordinary ventilating 

 system. By providing slides for the hood 

 outlets, or so-called chemical vents, econ- 

 omy in the speed of the motor may be 

 brought about. 



Undoubtedly glazed tile is the best ma- 

 terial of which to construct the chemical 

 vents. These should be set in hot tar. 

 With buildings constructed of steel and 

 stone, it is not easy, where sizes of the 

 vents are variable, to secure a material 

 properly burned, and it is difficult to hold 

 it in place. We therefore devised a lining 

 for our ducts which we think is satisfac- 

 tory. The ducts may be cut to pass ob- 

 structing steel members or to follow any 

 line that is desired. These ducts are essen- 

 tially a frame of galvanized iron on the 

 inside of which a lattice work of expanded 

 metal is riveted. Upon this is placed 

 from five eighths to three fourths of an 

 inch of a cement containing some plaster 

 and a sodium silicate composition, which 

 sets to a very rigid mass. It is acted upon 

 very slightly by acids. Of course, hydro- 

 fluoric acid attacks it as it does glazed 

 tiling. This is subsequently covered, after 

 thoroughly drying out, with three coats of 

 an acid-proof paint. That which we used 

 was devised by Mr. Maximilian Toch. It 

 may not be uninteresting to give an account 

 of some of the tests to which a preliminary 

 sample duct was subjected before the in- 

 structions were given to proceed. A joint 

 was made and was placed in contact with 

 concentrated sodium hydroxide, concen- 

 trated ammonium hydroxide, and concen- 

 trated hydrochloric, sulphuric and nitric 

 acids. It was slightly affected by the con- 

 centrated nitric acid. The coating was 



furthermore subjected to the vapors of boil- 

 ing sulphuric acid and to a stream of 

 chlorine. We felt that if it would with- 

 stand these reagents it could be safely 

 placed in the building. The interior of 

 these flues may be repainted from time to 

 time by closing all the vents on any one 

 line of the system, except the last one. 

 Atomized acid-proof paint may be swept 

 through the system by having the fan going 

 at full speed. The large duct, five feet in 

 diameter, at the end of the system, should 

 be arranged to collect condensed moisture 

 in a trough from which it may flow into the 

 chemical drain. A man-hole placed at this 

 point allows a cleaner to enter and wash 

 down the walls by means of a hose. 



The hoods, preferably constructed of 

 wood, should have a stone base slightly 

 inclined to the rear, where an outlet is pro- 

 vided to the chemical drain. We have 

 found that a cup east of lead containing 

 nine per cent, of antimony is most satis- 

 factory for a connection to the cast-iron 

 chemical drain to which reference has been 

 made. Muthmann has constructed the 

 drain pipes in the new Munich laboratory 

 of this alloy. It is somewhat expensive, 

 but exceedingly attractive, to have the rear 

 of the hoods faced with glass tiling, and 

 the vents made of white porcelain. But if 

 they can do it in Childs's restaurants, I 

 thought we could. Each hood is provided 

 with two vents, one about twelve inches 

 from the floor of the hood, and the other 

 about twelve inches from the top. These 

 vents are provided with sliding porcelain 

 doors so that they may be closed when not 

 in use. 



HYDROGEN SULPHIDE 



Hydrogen sulphide is delivered through- 

 out the laboratory from a central genera- 

 ting plant in the basement. The Parsons 



