io6 MARINE I.IGHTING EQUIPMENT OF THE PANAMA CANAL. 



The high quahty of the porous mass can only be obtained by a slow and 

 laborious process which makes the substance light and porous, yet solid and 

 enduring. 



In order to obtain the highest solvent efficiency, only the purest acetone 

 must be used. 



Finally, the acetylene must be thoroughly purified and dried, to meet 

 the severe requirements of lighthouse service. 



INFIvUENCE OF TEMPERATURE. 



A notable feature of dissolved acetylene is that its usefulness is inde- 

 pendent of the temperature. Acetone will not freeze ; the gas accumulator 

 can therefore be used in the coldest climates. For example, more than fifty 

 dissolved acetylene lights have been installed in Alaska, and some of these 

 installations operate the year round. 



It should, however, be observed that changes of temperature, although 

 in no way interfering with the usefulness of the gas accumulator, cause 

 corresponding changes of pressure inside the accumulator. The solvent 

 capacity of acetone varies according to the temperature in such a manner 

 that while it amounts to 25 times its own volume at 59° F. (15° C.) it grows 

 less at higher temperatures, so that at 122° F. (50° C.) it will be 50 per cent 

 less, that is, only 125 times its own volume, whereas it becomes greater at 

 lower temperatures, so that at about —4° F. ( — 20° C.) it will be double, that 

 is, 50 times its own volume. With a given quantity of gas in an accumulator, 

 the change in the solvent capacity at various temperatures will reveal itself 

 by corresponding variations in the pressure; when the temperature rises 

 the pressure will gradually rise, so that at 122° F. it will be twice as much 

 as at 59° F. ; when the temperature falls the pressure will gradually decrease 

 so that at about —4° F. it will only be half of what it was at 59° F. 



These variations of the pressure will only slightly affect the gas quantity 

 at disposal ; however, every atmosphere's pressure indicated by the pressure 

 gauge does not, at all degrees of temperature, represent the same quantity 

 of gas at disposal; at 59° F. it represents 10 times the volume of the accu- 

 mulator, at —4° F. it represents 20 times that volume, and so on. As the 

 porous substance is not a very good conductor of heat, only a prolonged 

 change in the temperature will materially affect the temperature in the 

 interior of the accumulator. 



