Ammonia in the Rust of Iron, 191 



3d. That the differences which soaps present, in respect 

 to hardness and softness, inodorous and odorous, are now 

 explained. In analysing a greater number of soaps than 

 those which are prepared for the wants of life, I have reduced 

 them to a small number of saline species. 1 have shown that 

 the type of hard soap is the stearate of soda, while the type of 

 soft soap is the oleate of potash ; that consequently, a soap 

 with a base of soda is the harder in proportion to the excess 

 of the stearic over the oleic acid which it contains; and a soap 

 with a base of potash is the softer in proportion to the oleic, 

 over the stearic or margaric acid. The various odours of 

 many kinds of soap, are due to principles quite different from 

 stearic, margaric, and oleic acids, since the latter may be com- 

 pletely isolated from the former. 



4th. That we may not only fabricate soaps, more hard or 

 more soft than those now in commerce, but also, by saponify- 

 ing mixtures of stearine and oleine, derived from fat bodies 

 extremely different from each other, imitate perfectly the 

 soap of any given kind, of fat; and I have already good rea- 

 sons for believing that industry will make a happy application 

 of these discoveries. — Idem, Mai 1823. 



26. Ammonia in the Rust of Iron. — M. Vauquelin informs 

 us that being called upon by one of the Judges of Paris, to 

 determine whether certain red spots found upon the blade of 

 a sword, which it was suspected had been employed in a 

 case of murder, were produced by blood, he detached with 

 the point of a penknife a small portion of the red matter, and 

 heated it in a bent tube closed at one end, and into which he 

 had introduced a strip of tournsol paper reddened by an acid, 

 and moistened. A vapour arose from the heated substance 

 which changed the red of the paper to blue. A second ex- 

 periment made with a similar material taken from the blade of 

 a knife which it was thought had been used for the same pur- 

 pose, produced exactly the same effect. A physician who was 

 consulted on the subject did not hesitate to affirm that the red 

 matter on these instruments was blood, but this excellent 

 chemist having still some doubts as to its nature, thought best 

 to treat a little common rust in the same way, and a piece of 

 iron found by chance in the cabinet of the judge supplied the 

 means.. 



