148 ANNUAL OF SCIENTIFIC DISCOVERY. 



paper, about 22 by 18 inches. It is thin, colorless, transparent, 

 exceedingly pliant, possesses a fine surface, and is water-joroof, or 

 nearly so, not being affected by fluids until after long treatment, 

 and then only slightly. It is exceedingly tough, bearing consider- 

 able strain without tearing, and is slightly elastic, stretching a 

 little when pulled. 



The multiplicity of purposes to which a material having most 

 of the properties of glass without its frangibility, and which might 

 be called flexible glass, may be applied in photography, will occur 

 to most readers. 



At present we have only had opportunity for experiment in two 

 directions with the sheets sent to us. We have employed it as a 

 protective surface to small pictures, in a manner similar to that in 

 which sheets of collodion and gelatine have been used, and also as 

 a substitute for glass in taking negatives. For the first purpose 

 its application is simple and easy. A sheet of the material, having 

 been cut to the required size, is immersed for a few minutes in 

 clean water, or dilute alcohol and water would be better still. 

 The picture to be protected is then wetted, either by holding under 

 a tap, or immersing in a dish of water. The wet, vitreous sheet 

 is then brought into contact with the wet surface of the print, 

 which till then is kept in a horizontal position ; the two being then 

 raised into a vertical position, and drained, the surfaces come into 

 close contact, the w^ater running out from between them driving 

 away all air-bubbles. A sheet of paper is placed over the suiface, 

 and the whole rubbed well down to secure firm contact. The 

 protected priiit is then dried under pressure. The appearance of 

 the finished print is very similar to that of a print "enamelled" 

 with gelatine and collodion. 



In our attempts to use the vitrified sheet as a support in produc- 

 ing negatives, we proceeded as follows : A piece of the sheet 

 is cut about a quarter of an inch less than a plate of glass of any 

 suitable size. The vitrified sheet is moistened at the back, and 

 placed on the plate of glass, to which the moisture causes it 

 readily to adhere. It is then coated with collodion', wiiich, flowing 

 over the edge of the sheet and up to the edge of the glass, pro- 

 tects it from displacement in the nitrate bath. This done, the 

 manipulations are conducted in the usual w^ay until the negative 

 is finished, when it is easily removed from the glass by running a 

 penknife round the edge and lifting away the negative on its limp 

 transparent support. There are certain precautions necessary in 

 these manipulations. It is important to see that the pellicle is 

 quite flat on the glass, without wrinkles, and that the edges do not 

 curl up so as to permit the collodion to flow under between the 

 vitrified sheet and the glass. 



The most curious difficult}^ we met in usihg the new material 

 as a substitute for glass in taking negatives is one which we hope 

 is exceptional, or in any case we are disposed to believe it is 

 avoidable. It is this, — the exposure required is much longer. 



Wc may here mention an ingenious application which Mr, 

 Woodbury has for some time contemplated making of such a 

 material as this. He proposes to sensitize a long strip of it by 



