Ammonium carbonate, when above a certain amount, also prevents the commencement of nitrification. The strongest solution in which nitrification has at present commenced contained ammonium carbonate equivalent to 368 milligrammes of nitrogen per liter. This hinderance of nitrification by the presence of an excess of ammonium carbonate effectually prevents the nitrification of strong solutions of urine, in which, as already mentioned, ammonium carbonate is the first product of fermentation. Far stronger solutions of ammonium chloride can be nitrified than of ammonium carbonate, if the solution of the former salt is supplied with calcium carbonate. Nitrification has in fact commenced in chloride of ammonium solutions containing more than two grammes of nitrogen per liter. The details of the recent experiments, some of the results of which we have now described, will, it is hoped, shortly appear in the _Journal_ of the Chemical Society of London. Harpenden, July 21. * * * * * ANILINE DYES IN DRESS MATERIALS. By Professor CHARLES O'NEILL. Twenty-eight years ago Mr. Perkin discovered the first of the aniline dyes. It was the shade of purple called mauve, and the chief agent in its production was bichromate of potash. This salt is not actively poisonous, and no one thought of attributing injurious properties to materials dyed with the aniline mauve. Next in chronological order came magenta red. It was first made from aniline by the agency of mercurial salts, and afterward by that form of arsenic known to chemists as arsenic acid. The fact that this at one time fashionable color was prepared by means of an arsenical compound was spread through the country in a very impressive manner by the great trial as to whether the patent was valid or not, all turning upon the expression in the specification of "dry arsenic acid," and the disputes of scientists whether this expression meant arsenic acid with or without water. The public mind had been for some time previously exercised and alarmed by accounts of sickness and debility caused by arsenical paper-hangings; it was, therefore, easy for pseudo scientists to create an opinion that the magenta dye must be also poisonous, and that persons wearing materials dyed with this color were liable to absorb arsenic and suffer from its action. Ever since there have been, at intervals, statements more or less circumstantial, that individuals have suffered from wearing materials dyed with some of the artificial dyes. At the present time these statements are emphasized by the exhibition at the Healtheries of models of skin diseases said to be actually produced by the wearing of dyed garments. Whether it be true or not that any form of skin disease has been produced by the wearing of dyed articles of clothing is simply a question of evidence, and there is evidence enough to show that individuals have experienced ill effects who have worn clothing dyed with artificial colors.