92 
Proceedings of the Royal Society 
By the process now described sodic nitroprusside can be made 
in any quantity, and without the loss of any of the Cyanogen pro- 
ducts. The reaction involved in the above process is extremely 
simple. The first portion of tartaric acid removes an atom of 
potassium, and substitutes it by hydrogen. The second portion 
of acid acts on the sodic nitrite, liberating nitrous acid : — 
2FeCy 6 K 2 H + 2N0 2 H = 2H 2 0 + 2FeCy 5 N0K 2 + Cy 2 . 
The sodic chloride and tartrate exchange their sodium for the 
potassium of the nitroprusside, partly on addition, and more largely 
on crystallization. 
3. Note on the Reality of the Roots of the Symbolical 
Cubic which expresses the Properties of a Self-conjugate 
Linear and Vector Function. By Professor Tait. 
Hamilton has shown that if 
<Pp = 2aS (3p + A p, 
where a and f3 are given vectors, and A a given scalar, we have 
(<p :i - m, <p 2 + m$ — m)p = 0, 
where m, m 1) m 2 are scalars depending only on <p. 
When the function <p is its own conjugate , i.e., when 
S p<p<r = S<x£>p, 
p and a being any vectors whatever, the vectors for which 
0-2> = 0, or <pp\\p, or Vp<pp = 0, 
form in general a real and definite rectangular system. This, of 
course, may in particular cases degrade into one definite vector, and 
any pair of others perpendicular to it ; and cases may occur in which 
the equation is satisfied for every vector. 
Suppose the roots of m g = m + m l g + m 2 g 1 + g 3 = 0 to be real and 
different, then 
PPi = ffiPi ) 
<PP, = ffiPi | where Pl , p 8 , Pi are definite vectors. 
<P,\ = 9zPs I 
