304 The N.Z. Journal of Science and Technology. [July 
In specimen H of shipment 2 a slight coloration was noticed in one 
patch, but apparently there was no general penetration in the section where 
the cut was made. 
Insulators by Maker Y. 
TEST No. 3. 
This experiment was made with nine specimens of an insulator made 
by maker Y. These specimens were chosen from all parts of the insulator, 
and two of them, G and J, were somewhat thick irregular lumps of porcelain. 
In Gl before the test was made a slight hole was noticed, which had the 
appearance of being the entrance to a sort of channel formed by an air- 
bubble imprisoned in the clay in process of manufacture, and drawn out 
into an elongated duct. These were noticed more than once in this make 
of insulator. With these nine specimens of Y make one small piece of 
an X insulator was included, as from its appearance porosity was suspected. 
An average pressure of 2,0501b. per square inch was maintained for fifty 
hours. 
Specimen. 
Weight dry. 
Density. 
Increase in 
Weight. 
Grammes. 
Grammes. 
Y A 
. . 93-534 
2-281 
•013 
Y B 
. . 51-750 
2-288 
•000 
Y C 
. . 42-116 
2-289 
•002 
YD 
. . 44-594 
2-289 
•004 
YE 
. . 73-394 
2-316 
•016 
Y F 
. . 62-832 
2-285 
•000 
Y G 
. . 92-076 
2-278 
•030 
Y H 
. . 44-723 
2-286 
•001 
Y J 
. . 90-592 
2-283 
•044 
X special piece 
. . 42-957 
2-353 
•120 
The specimens were afterwards broken in chosen lines and examined. 
In the case of the nine specimens of *Y make no penetration of dye into 
the body of the material was noticed, except in the case of Gr ; but several 
tiny holes revealed themselves—probably the entrances to small air-bubbles 
imprisoned during the manufacture. These were more evident in the thick 
crown pieces, A, G, and J, than in the thinner C “ petticoat ” pieces. It 
is probably the filling-up of some of these with liquid that led to the 
comparatively large increase in weight. 
On the other hand, the picked specimen of X manufacture showed* 
most distinct general penetration, as was expected,' but as the character 
of this penetration was better brought out by the next experiment nothing 
more will be said of it here. 
Insulators suspected of being Porous. 
TEST No. 4 
In this test samples of three insulators were taken, all of which 
were suspected of being porous. They had been on the transmission¬ 
line for some three years, had been taken down because they were 
suspected, and had been subjected to “ Megger ” tests and “ fifty- 
cycle-pressure ” tests, of which the following details have been supplied 
to me. 
