ul 
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romeo oe i 
‘ 
' 
Ammonia in the Rust of Iron. 491 
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 asmall 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 o 
many kinds of soap, are due to principles quite different from 
stearic, margaric, and oleic acids, sincethe 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. 
25. 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 o 
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. » 
