Note 269 — Chapter XVI

This may be readily proved by the following simple but instructive experiment:—Take two pairs of watch-glasses; into one pair put a solution of nitrate of silver, into the other a weak solution of iodide of potassium; connect the silver solution of each pair with the potash one by a film of cotton, and carry a platina wire from one glass into the other. Place one series in sunshine, and the other in a dark place. After a few hours it will be found that the little galvanic arrangement in the dark will exhibit, around the platina wire, a very pretty crystallization of metallic silver, but no such change is observable in the other exposed to light. If a yellow glass is interposed between the glass and the sunshine, the action proceeds as when in the dark. This experiment is naturally suggestive of many others, and it involves some most important considerations.