POTTERY* 
55 ' 
all over it. When put in the kiln the heat 
causes the lead in the glaze to unite with the 
silica and alumina of the clay and a water- 
proof coating (in reality a variety of glass) is 
formed. 
To prepare the glaze, strongly heat some 
ordinary lead in an iron pot ; it will melt at 
about 330 P C, and when further heated will 
turn into a yellowish powder (lead monoxide). 
Drinking water coolers. The most popu- 
lar, perhaps, of our potters’ wares are the 
earthenware jars, locally known as “ monkeys” 
and in very general use. They should cer- 
tainly always be used when ice is not airnil- 
able. The water, which slowly percolates 
through the porous earthenware, is readily 
evaporated (especially on a windy day) and 
the loss of Jieat due to this process greatly re- 
duces the temperature of the water. 
In order to test the real Amine of these 
“ monkeys,” for cooling purposes, the writer 
put equal quantities of water into one of these 
earthenware jars and a glass vessel and placed 
both in the hot sun on a still day. After ex- 
posure for one and a half hours the water in 
the monkey was 10 °F. cooler than that in the 
glass vessel. The water in both vessels was, 
of course, of the same temperature when the 
experiment was started. 
