512 Prof. Faraday on the Eaperimental Relations 
For the same reason as in the last article, vu, and tu) cannot 
contain any inverse powers of a, y, 2. 
Thus the ultimate form of the required solution is 
w=q'z(aa*+4ba%y*+cy*) +3 (Ax?+ Quay +vy*) + (ae+Py+yz2) +8, 
where a, 8, y, 5 are arbitrary constants, 
10. Again, let it be proposed to integrate the system 
du 2du _ 5 oe 
Sg ee eet 
du 2 du ba? 
Biitiies eran ag 
Multiplying the first equation by x, the second by y*, and add- 
ing, as before, we get 
V(V +1) .u=2(ax* + bya? + cay? + dy’), 
whence ; 
u=1 (aa + byx? + cay? + dy®) +a, 
the arbitrary constants in the second arbitrary function being of 
necessity reduced to cipher. 
Trinity College, Dublin, 
October 10, 1857. 
LIX. LEzperimental Relations of Gold (and other Metals) to 
Light.—The Bakerian Lecture. By Micuart Farapay, Esq., 
D.C.L., F.RS., Fullerian Prof. Chem. Royal Institution, §c. 
[Concluded from p. 417.] 
Diffused particles of gold—production—proportionate size—colour 
—aggregation and other changes. 
Finch competent to reduce gold from its solution are very 
numerous, and may be applied in many different ways, 
leaving it either in films, or in an excessively subdivided condition. 
Phosphorus is a very favourable agent when the latter object is 
in view. Ifa piece of this substance be placed under the surface 
of a moderately strong solution of chloride of gold, the reduced 
metal adheres to the phosphorus as a granular crystalline crust. 
If the solution be weak and the phosphorus clean, part of the 
gold is reduced in exceedingly fine particles, which, becoming 
diffused, produce a beautiful ruby fluid. 
This ruby fluid is well obtained by pouring a weak solution 
of gold over the phosphorus which has been employed to produce 
films, and allowing it to stand for twenty-four or forty-eight 
hours; but in that case all floating particles of phosphorus 
should be removed. If a stronger solution of gold be employed, 
