26 



MEDICINAL USES OF HOPS. 



Hop resin and the essential oil are not identical; the 

 former is soluble in ether, the latter is not. In the course 

 of long exposure it becomes insoluble. The gum and ex- 

 tractive colouring matter are of little use. The mineral 

 constituents of hops dried at 100 are : ash, 9 to 10 per 

 cent.; 15 per cent, of phosphoric acid; 17 per cent, of 

 potash, &c. 



Hops have recently been found to be a photo preservative. 

 Numerous experiments having been made in the emulsion 

 process, the desideratum has been found in ordinary hops 

 preferably the variety known as Bavarian, which seems 

 stronger in certain qualities than the English hop. Accord- 

 ing to the ' British Journal of Photography ' : 



" Two ounces of hops are infused for one hour in 20 ounces 

 of water at a temperature of 170 Fahr., and the whole then 

 turned into a cloth, and the liquid pressed out. When cold, 

 20 grains of pyrogallic acid and the albumen of two eggs are 

 added, and the mixture is well shaken for ten minutes. It is 

 then filtered into a dish and used in the ordinary way ; or, if 

 only a few plates are to be prepared, a smaller quantity may 

 be made, and poured off and on several times. Plates pre- 

 served with this solution dry perfectly hard, have a fine gloss, 

 and yield negatives of very high quality. The colour is a 

 rich greenish-brown, and so non-actinic that over-develop- 

 ment must be carefully guarded against. Although the 

 solution can be easily made, it is desirable that, if possible, it 

 should be made to keep, and therefore we have added carbolic 

 acid and salicylic acid to separate quantities, and shall note 

 the result on a future occasion. 



"Meantime we consider the hop preservative, as above 



