M. C. Lea — Endothermic Decompositions by Pressure. 419 



Potassium Ferridcyanide. — Pure paper was imbued with a 

 dilute solution of this salt. After thorough drying it was laid 

 on a glass plate aud 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 sta- 

 ble than the ferridcyanides. When sodium nitro prusside 

 paper was treated with pressure, followed by appropriate rea- 

 gents, 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. Color dark purplish gray. 



Platinic Chloride. — After drying and marking, the paper 

 was thoroughly soaked in water and dried. The marks were 

 very distinct, of a yellow color. 



Ammonium P iatinichlor id 'e.— -Marks very visible. Contin- 

 ued 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 carbo- 

 nate 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. 



Twpeth Mineral. — Mercuric sulphate was dissolved in water 

 with the aid of sulphuric acid. Paper was soaked in the solu- 

 tion, 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. 



Ferric Alum {ammonia). — Paper imbued with solution of 

 this salt dried and marked was immersed in solution of potas- 

 sium ferridcyanide. The marks came out blue showing that 

 the ferric salt had undergone partial reduction. 



