302 The N.Z. Journal of Science and Technology. [July 
The Porsity of Porcelain, with Special Reference to High-pressure 
Insulators for Electric Transmission-lines, by C. C.Farr. 
The following tests arose out of a desire expressed to me by the 
engineers of the Lake Coleridge electric-supply system that a method 
should be devised by which it could be ascertained whether or not the 
porcelain of which the insulators on the Lake Coleridge transmission¬ 
line were made was of a porous nature. Some of the failures of these 
insulators seemed ascribable to this cause only, and positive proof of the 
fact was desired. It so happened that I had in the physical laboratory 
of Canterbury College a gas-compressing pump capable of compressing 
up to 2,250 lb. per square inch, and it was apparent that this might be 
used with advantage for the purposes of the test. 
It was decided after some discussion to immerse specimens cut from 
the insulator in a coloured solution (fuchsin was chosen, though red ink 
does as well) and subject them to an air-pressure of somewhere in the 
neighbourhood of 2,000 lb. per square inch for a period to be determined 
by experiment. For this purpose a solid block of mild steel was obtained, 
of rectangular cross-section and of dimensions 5 in. by 5 in. by 9 in., 
and into this a cylindrical cavity 3 in. in diameter and 6J in. deep was 
bored. On to this a well-fitting cover of the same steel 1 in. thick was 
bolted by eight bolts, and this with the aid of a leather washer between 
the cover and the pressure-chamber was found to be capable of 
maintaining a pressure in the chamber of 2,000 lb. for many hours. 
Suitable valves for shutting off the pressure-chamber from the pump 
were inserted, and a pressure-gauge for determining the pressure in the 
chamber. 
Preliminary experiments showed that signs of penetration of the fuchsin 
solution into the porcelain of some specimens was to be noticed in about 
twenty-four hours. 
Specimens from two shipments of insulators made by maker X were tested, 
and from one by maker Y. These specimens were pieces cut from selected 
places in the insulator, and weighing from 25 to 100 grammes each. They 
were first dried as well as could be done by maintaining them at a tempera¬ 
ture of roughly 150° C. for some forty-eight hours, in an oven supplied 
by the Public Works Department. They were then carefully weighed dry 
and then in water, so that the density might be determined. About ten 
at a time were next placed in the pressure-chamber, which was then filled 
with fuchsin solution. Air-pressure of the intensity mentioned in the 
tests was maintained in the chamber for the periods stated in the tests 
to be quoted. The samples were then taken out and washed and dried 
with a cloth, and re weighed to determine the weight of the absorbed 
moisture. As a check on the increase and to acquire further information 
the specimens were then cut at a selected line (we learnt how to do this), 
when the passage of the fuchsin solution into the material of the insulator 
could be seen by the red coloration, if any. 
Comparative Tests of Insulators from Shipments 1 and 2 of 
Insulators by Maker X. 
Ten specimens were cut from the second shell of an insulator chosen 
from each of these shipments. Five were from the glazed part of the 
shell of each insulator, and five from the unglazed crown. The ten 
* At the Congress this paper was accompanied by a demonstration by G. F. Ferguson. 
