TRI'lATMENT FOR TliXTILIi lySfLATIOS 243 



from the drying chamber, cooled down to the same temperature, con- 

 taining acetone vapors in addition to the constituents of the room 

 atmosphere. The different thermal conductivities of the gases around 

 the two coils cause a difference in temperature and therefore a change 

 in resistance of the platinum coils which causes a reading on the 

 galvanometer. The instrument is calibrated to read directly in per 

 cent acetone. If a reading greater than the allowed maximum of 1.8 

 per cent concentration is encountered, a gong is sounded and the head 

 is immediately switched to half speed until the trouble is located and 

 remedied. The percentage of acetone concentration can be varied by 

 increasing or decreasing the amount of room air drawn through the 

 machine to the recovery system. 



To avoid all sparks in the main rooms, where some acetone vapor 

 may exist, a separate control room with entry from the outside only is 

 provided. Lead covered cables running through sealed ducts connect 

 the machines with the control room and all fuses and relays are in this 

 room. Switches on the machines are oil immersed or fully enclosed 

 and gas tight. A magnesite floor is provided to prevent the striking 

 of sparks from reels or tools that may be dropped and brass floor plates 

 are used instead of steel for the same reason. 



Although the present installation is well protected from fire and 

 explosion, there are still a number of characteristics of acetone that 

 are not well known, and it is probable that more exact knowledge 

 would make it possible to achieve safety in future installations at less 

 expense. A study is therefore under way in cooperation with the 

 Bureau of Mines at Pittsburgh to determine these unknown charac- 

 teristics of acetone. Among the unknown quantities are the exact 

 lower limit of acetone vapor concentration that is explosive under con- 

 ditions such as are encountered in our drying chambers, the effective- 

 ness of various relief openings, the probability of ignition from various 

 sources, especially static sparks, and the force of explosions possible 

 from various concentrations. 



Recent Developments 

 A new coating machine has been developed that operates at a higher 

 speed, is simpler to operate and is still better safeguarded against fire 

 and explosion. It consists of eight coating units on a common base, 

 four units being on each side. Instead of electrical heating elements in 

 each coating unit one steam heater supplies hot air to a number of 

 machines. The temperature is automatically controlled at the heater, 

 leaving the operator free to watch the supply and take up of the wire. 

 A wire speed of 240 feet per minute has been obtained compared to 



