GLASS RESISTS HEAT

Opotiki News, Volume X, Issue 1045, 11 November 1947, Page 2

GLASS RESISTS HEAT

NEW BRITISH PRODUCT One of the great'disadvantages of glass for certain purposes, particularly for cinematograph projectors, has been that in lenses while ittransmits most of the light, it- also radiates touch* of the energy, and so is likely to burn such materials as film.

This is true, -because all ordinary sources of white light radiate a certain amount of energy; at “infrared” frequencies, and the heat is absorbed by- such materials as film,, which is likely to burn unless the exposure is very short. To try to overcome this difficulty, filters hav e long been- used, but these are often inconvenient, and are not always effective; 1

A hew heat-absorbing glass known as “ON 19”, has now been produced by the British firm of Chance Bros., which is said to be particularly suitable for projectors and to show a great advance on all previous glasses.

It is claimed that with an ordinary gas-filled lamp of the type often used for projection, this new glass, ON 19, will transmit 81 per cent, of the visible light and only 4.V per cent, of the heat. The glass is also said to be almost colourless and to bo durable and heat resistant-. On account of the fact that- the glass is liable to contain air bubbles, - it is intended at present for use only as a filter, but it will have many important uses in. scientific"’ equipment.