354 THE AMERICAN MONTHLY [Kov 



the ribs and vertebrae will be distiuftly visible. Several 

 materials have been suggested for the manufaclure of 

 these screens but probably tlie most sucL-e.sst'ul has hc-eu 

 Platino-cyanide of Potassium. Tliis salt, however, varies 

 very considerably in its fluorescent properties and quan- 

 tities from the same manufacturer purchased at separate 

 times do not yield uniform results. The method of pre- 

 paration -is as follows : The Platino-cyanide is ground as 

 finely as possible with a pestle and mortar. It is then 

 mixed with weak clear gum water and spread evenly ui)on 

 a thin sheet of cardboard. One coat alone at a time 

 should be given and allowed to dry; two or three coats 

 are usually sufficient. Owing to the expense of the 

 material and the chances of failure in preparing, it has 

 usually been found more economical to purchase ready 

 made screens. Calcium tungstate was the material sug- 

 gested by Edison for these screens but it does not com- 

 pare favorably with Platino-cyanide of Potassium. 



A new screen has recently been placed on the market 

 by Watson & Sons, London, which surpasses in brilliance 

 others that have been so far made. The material is a 

 secret preparation but with a good focus tube it enables 

 the bones (ribs, vertebrae, etc.) of an adult person to be 

 seen clearly. 



Apparatus : — At the outset extravagant rumors were 

 set afloat as to the cost of the necessary instruments, but 

 the outfit has now been reduced to a battery, an induc- 

 tion coil and a vacuum tube. 



Additional but not absolutely necessary apparatus, 

 would be a holder for the tube, and a fluorescent screen. 

 The battery may consist of either Bunsen's or Grove's 

 bells or a 4 cell accumulator giving 8 volts and a current 

 of about 8 amperes. 



The Coil: — A Ruhmkorff Induction Coil giving a 3iuch 

 spark only is sufficient for obtaining Radiographs of the 

 arm, leg, etc. but if deeper structures are to be dealt with 



