Decompositions obtained by Pressure. 37 



however, is a somewhat different matter from actual and 

 visible decomposition following each stroke of the rod, a 

 result which may be obtained with various salts of gold, 

 mercury, silver, and other metals. 



Potassium Ferridcyanide. — Pure paper was imbued with a 

 dilute solution of this salt. After thorough drying it was 

 laid on a glass plate, and marks were made with a glass rod 

 in the manner just described. These marks were immediately 

 visible, and when the paper was plunged into dilute solution 

 of ferric ammonia alum or of ferric chloride they became dark 

 blue. It is probable that the decomposition here effected was 

 twofold (see above). — The nitroprussides appear to be much 

 more stable than the ferridcyanides. When sodium nitro- 

 prusside paper was treated with pressure followed by appro- 

 priate reagents, no indications of decomposition were obtained. 



Auric Chloride. — Paper imbued with a solution of auric 

 chloride and marked in the manner described was thoroughly 

 soaked in water to remove, as far as possible, the rest of the 

 gold salt. The marks were very distinct and gradually 

 gained with time. Colour dark purplish grey. 



Platinic Chloride. — After drying and marking, the paper 

 was thoroughly soaked in water and dried. The marks were 

 very distinct, of a yellow colour. 



Ammonium Platinichloride. — Marks very visible. Con- 

 tinued to slowly deepen, and in a few weeks were almost 

 black. 



Silver Carbonate. — The traces of the rod were brown. 

 When the paper was placed in ammonia the carbonate dis- 

 solved, but the marks resisted the action of the ammonia and 

 remained. 



Silver Phosphate. — Action very similar to the preceding. 



Silver Arsenate. — Similar action. 



Silver Tartrate and Oxalate. — These salts gave analogous 

 results to the preceding, but not so well marked. The car- 

 bonate, phosphate, and arsenate show this reaction best, and 

 about equally well. What is rather curious is that silver 

 chloride does not exhibit a visible action. 



Mercuric Oxide. — Paper imbued with a saturated solution 

 of mercuric nitrate and then treated with solution of potash 

 and dried shows this reaction very distinctly. Mercuric 

 oxide appears to be quite sensitive to light. 



Turjoeth Mineral. — Mercuric sulphate was dissolved in 

 water with the aid of sulphuric acid. Paper was soaked in 

 the solution, allowed to become nearly dry, and then washed. 

 This paper showed the reaction very moderately, but the 

 marks were brought out more strongly by immersion in 

 ammonia. 



