English: Cavendish's method for the isolation of Argon. The gases are contained in a test-tube (A) standing over a large quantity of weak alkali (B), and the current is conveyed in wires insulated by U-shaped glass tubes (CC) passing through the liquid and round the mouth of the test-tube. The inner platinum ends (DD) of the wire may be sealed into the glass insulating tubes, but reliance should not be placed upon these sealings. In order to secure tightness in spite of cracks, mercury is placed in the bends. With a battery of five Grove cells and a Ruhmkorff coil of medium size, a somewhat short spark, or arc, of about 5 mm is found to be more than favorable than a longer one. When the mixed gases are in the right proportion, the rate of absorption is about 30 cm³ per hour, about thirty times as fast as Cavendish could work with the electrical machine of his day. Where it is available, an alternating electric current is much superior to a battery and break, allowing the absorption in the apparatus to be raised to about 80 cm³/hour.
Illustration from 1911 Encyclopædia Britannica, article Argon.