1644 REFRIGERATION AND REFRIGERATOR INSULATION ON BOARD SHIP. 
For thick walls and poor conductors, ¢ is so small that it can be neglected. Rietschel 
gives values of t, for windows, as 36; for brickwork 5 inches thick, as 14; for brickwork 
30 inches thick, as 5; for wooden doors, as 2. 
The following table expresses the amount of heat transmitted, expressed in English 
units, for different thicknesses, and is in such close accordance with results obtained in 
practice, that it can be used as a basis of calculation for design of insulating materials of 
either balsa wood or cork of the highest quality. 
““Coefiicient of heat 
“Specific conductivity” Thickness in inches transmission’’ 
B. T. U. 
e=0.39 ae 2=0.242 per hour 
e=0.35 — A=0.143 per hour 
e=0.35 a A=0.1015 per hour 
Mr. A. P. Lunpin, Member (Communicated) :-—The writer’s attention was drawn to 
balsa wood many years ago, during voyages to tropical countries, viz., Central and South 
America, Central Africa, and also India, in all of which the same species can be found; and 
he first remarked it when a number of natives came floating down a river on a raft made 
up of balsa logs. The logs were covered more or less with bark, and where this was chipped 
away the hard surface still remained, which is found on the outside of balsa logs, under the 
bark; the ends were covered with tar, or some waxy substance. 
The natives, particularly in Central and South America, use such rafts to float their 
products to the sea coast, and seldom use them more than once; for one reason, because it 
would be difficult to bring the rafts up against the stream, and because the wood absorbs 
water very readily and the raft is more or less water-logged after arriving. Of course, in 
solid logs, with the ends closed up, the absorption is not so rapid as when balsa is cut up in 
planks and freed from bark. 
Later, when engaged in the life-saving equipment business, it was brought to the writer’s 
attention that some crude attempts had been male to use balsa in life-preservers. On taking over 
a boat shop in Long Island City, a quantity of balsa was found there, and, on inquiry as to its 
purpose, it was learned that experiments had been made with it in life-belt manufacture, but 
that the wood absorbed water so rapidly that the belts had to be made two or three times as 
large as the ordinary cork life-belt to assure the required buoyancy. Subsequently, chemical 
experts were put to work to devise methods for making the wood non-absorbent. 
First, painting was tried, but, owing to the peculiar nature of the material, the paint was 
rapidly absorbed, and coating it over and over meant having just as much paint as wood, 
which added greatly to the weight. Then varnishing was tried, but, owing to the moisture 
left inside, the varnish cracked and blistered off. 
Next, several mixtures of paraffin, asphaltum, gilsonite, etc., were tried, which gave a 
fairly good outside coating, penetrating about 4 inch on the ends and about 75 inch on the 
sides, and the problem was apparently solved. However, before long it became evident that, 
owing to the cellular structure of balsa, which i mostly pith, and the great quantity of moisture 
sealed up in the wood by the impervious surface treatment, dry-rot developed even sooner 
than in the untreated balsa. 
