282 Sub- Lieut. A. L. Williams on the Electrical 

 III. Notes. 



(1) It was noted that the material was malleable at about 

 2000° C. 



(2) A specimen piece was rolled at this temperature into 

 a small rod 2*5 mm. in diameter for the purpose of ascer- 

 taining the specific resistance of the mixture. This was 

 found to be as follows : — 



25° C, Specific Resistance, 10,400 ohms. 

 30° C, „ „ 8,000 ohms. 



(3) An attempt was made to obtain a sample of the mix- 

 ture in the form of a very thin film for delicate temperature 

 measurements, etc., and it was found possible to squeeze it 

 out to about 1/1000 of an inch between platinum foil. It was 

 not possible, however, to separate the film from the foil; but 

 two pieces of foil cemented together by this fine film were 

 found to be extremely sensitive to heat. They quickly 

 responded to the action of infra-red rays from an arc about 

 one yard away, notwithstanding the comparatively large 

 volume of platinum to be heated first. 



It is thought that with suitable films of the copper-mica 

 mixtures enclosed in hydrogen it may be possible to use 

 them for signalling purposes. It is also suggested that these 

 films may be used instead of wires in microphones for sound- 

 ranging, as the changes of resistance, due to changes of 

 temperature^ are quite considerable, being some thousands of 

 ohms per degree centigrade with some samples. 



(4) Attempts were made to make thin sheets by mixing 

 the copper-mica material, finely powdered, with fine carbon^ 

 in the form of cane-sugar, and driving off the water by 

 heating. The resistance of the resulting material was 

 extremely high, but very regular thin sheets could be 

 obtained in this way. It is possible, when the density of 

 this mixture is increased by compression in an hydraulic 

 press, that it may be obtained in sheets, rods, or other forms 

 having a moderate resistance and yet possessing a high 

 resistance- temperature coefficient. 



5. , Attempts to cast the material in various forms were not 

 successful, partly owing to the difficulty in working with the 

 requisite high temperatures. The material, when molten, is 

 absorbed by such porous substances as porcelain, and if 

 glazed porcelain is used the glazing melts and mixes with the 

 material. It is possible that castings could be obtained by 

 using fused quartz as a moulding material. 



