154 
DE. EAEAEAT ON THE EXPEEB^E^^’AL EELATIOXS 
laid on glass for the terminals), a deposit of metallic gold in fine particles is produced. 
The densest parts have a dark slate-violet colour passing into violet and ruby-violet in 
the outer thinner portions ; a ruby tint is presented occasionally where the heat of the 
discharge has acted on the deposit. The deposited gold was easily removed by wiping, 
except actually at the spot where the discharge had passed. AMien these deposits were 
heated to dull redness they changed and acquired a ruby tint, which was very fine at 
the outer and thinner parts. The portions nearer the place of discharge presented ruby- 
violet and then violet tints, suggesting that accumulation of that which presented a fine 
ruby tint would, by stopping more and more light, transmit a ruby-’^iolet or violet ray 
only. Pressure with the agate surface had a like etfect as before, both with the heated 
and the unheated portions, e. with the violet and the ruby particles ; but the effect was 
not altogether so good, and the tint of the transmitted ray was rather a green riolet than 
a pure green. Still the difference produced by the pressure was veiy remarkable. The 
unheated particles at the surface, away from the glass, presented by reflexion almost a 
black ; being heated, they became much more golden and metallic in appearance. 
I prepared an apparatus by which many of the common metals could be deflagrated 
in hydrogen by the Leyden battery, and being caught upon glass plates could be 
examined as to reflexion, transmission, colour, &c. whilst in the hydi’ogen and in the 
metallic, yet divided state. The following are briefly the results ; which should be con- 
sidered in connexion with those obtained by employing polarized light. Copper: a 
fine deposit presenting by reflexion a purplish red metallic lustre, and by transmission a 
green colour, dark in the thicker parts, but always green ; agate pressure increased the 
reflexion where it was not bright, and a little diminished the transmission, rendering the 
green deeper, but not changing its character as in the case of gold. Tin gave a beautiful 
bright white reflexion, and by transmission various shades of light and dark brown ; 
agate pressure diminished the transmission and increased the reflexion in places before 
dull or dead ; the effect appeared to be due simply to the lateral expansion of the 
separate particles filling up the space. Iron presented a fine steel grey, or slate metallic 
reflexion and a dark brown transmission ; agate pressure gave the same effect as uith tin, 
but no change of colour. Lead : a bright white reflexion, the transmission a dark smoky 
brown ; agate pressure appeared to change this broum towards blue. Zinc : the reflexion 
bright white and metallic ; the transmission a dark smoky colour’ until portions of blue- 
grey, brown-grey and pale brown ; agate pressure tended to change the blue-grey to 
brown. Palladium: the reflexion fine metallic and dark grey; the transmitted light, 
where most abundant, sepia-brown; agate pressiue converted the tint in the thinner 
places from brown towards blue-grey. Platinum : the reflexion white, bright and 
metallic ; the transmission brown or warm grey with no other coloiu’s ; agate pressiu’e 
increased the reflexion and diminished the transmission as with tin. Aluminium: the 
reflexion metallic and white, very beautiful; the transmitted light was dark broun, 
bluish brown, and occasionally in the thinner parts orange ; agate pressure caused but 
little change. 
