226 PRACTICAL MICROSCOPY. 



Having obtained a suitable negative, it is easy to print 

 from this either upon carbon tissue or the ordinary sensi- 

 tised paper, which latter may now be bought ready prepared 

 at I s. per sheet. It will keep in good condition for months. 



After printing several shades darker than is finally 

 required, the prints are soaked in water to remove the free 

 nitrate of silver, and then put to tone in one of the following 



baths : 



I. 



Chloride of gold .. .. 15 grains 



Acetate of soda I oz. 



Water 80 oz. 



II. 



Dissolve one 15-grain tube of chloride of gold in 2 oz. of water. 

 Take I drachm of this solution, add 5 grains of tungstate of soda 

 and pour in 3 oz. of boiling water. Use the bath ten or fifteen 

 minutes after mixing j one grain of gold chloride will tone a sheet 

 of paper. 



III. 



Chloride of gold 15 grains 



Chloride of lime 15 grains 



Precipitated chalk I teaspoonful 



Water (boiling) 80 oz. 



This may be used at once. 



IV. 



Chloride of gold 7$ grains 



Perchloride of platinum 7i grains 



Acetate of soda I oz. 



Water 80 oz. 



After toning, the prints must be well washed and trans- 

 ferred to the fixing solution, which should be of the same 

 strength as that used for fixing the negatives. The prints 

 should be allowed to remain in this solution for ten minutes, 

 after which they are transferred to water, and washed until 

 perfectly freed from all traces of the hyposulphite. 



There are two applications of this art which may be of 

 great utility, viz. the preparation of wood-blocks for the 

 purpose of illustrating microscopical work and also for the 

 production of lantern transparencies. The greatest expense 



