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 *culty of breathing, evidently from obstruction of the larynx, and where the absence of abdominal pain, tension or vomiting affords a presumption that little injury has been done to the stomach, laryngotomy appears an advisable remedy, and has been known to give very great relief. But the patient may nevertheless die soon of the sympathetic disorder of the circulation.

II.—

Nitric acid is more frequently used as a poison abroad than in this country. But even in Britain it is not an uncommon cause of severe accidents and death.

Of the Tests for Nitric Acid.

1. When concentrated, nitric acid is easily known by the odour of its vapour, which is peculiar. When pure, the acid as well as its vapour is colourless; when mixed with nitrous acid it is of various tints, and generally yellow. The acid of commerce is at times rendered impure by sulphuric acid, a circumstance which must be attended to in applying the subsequent tests.—The simplest test for nitric or nitrous acid is the action of copper, lead, or tin. If any of these metals in small fragments, or powder, be thrown into either acid previously diluted with an equal volume of water, an effervescence takes place, which in the case of lead or copper is much accelerated by heat; nitric oxide gas is disengaged; and ruddy fumes of nitrous acid gas are formed when the gas comes in contact with the oxygen of the air. Another characteristic test, which has the advantage of being applicable on an extremely small scale, is morphia, the alkaloid of opium. This substance is turned in a few seconds to a beautiful orange-red colour by nitric acid, and after longer contact forms with it a bright yellow solution. No other acid has this effect. Muriatic acid, as Dr. O'Shaughnessey has remarked, does not act at all on morphia, and sulphuric acid chars and blackens it. When nitric acid is added to a solution of narcotin in sulphuric acid, the colour of the solution is changed from yellow to blood-red. When it is added to a solution of proto-sulphate of iron, the solution becomes brown, and the addition of sulphuric acid then alters the colour to violet. When it is added even in the most minute proportion to sulphuric acid, the addition of a few particles of the alkaloid brucia will render the whole fluid red, passing gradually to yellow.[D]—Many other characteristic tests might be mentioned; but those now specified are more than enough.

2. In a diluted state this acid is not so easily recognised as the other mineral acids, for it does not form any insoluble salt or precipitate with bases.