The workers in zinc and copper, especially in places where these metals are smelted, are subject to special forms of poisoning; but much of the lead poisoning or painters' colic, which is a disease causing severe pains in the intestines and paralysis, could be prevented by greater cleanliness. These diseases are, in many cases, not caused by breathing air impregnated with the solid particles given off in the process of working, but are the result of the want of cleanliness- of the workmen's hands, particles of white lead, etc., thus getting mixed with their food, so that greater cleanliness, in some cases, would do almost all that is required Workers in mercury, makers of mirrors and looking-glasses, also suffer from a similar kind of paralysis.

There is a beautiful paint containing arsenic and copper, which is very commonly used in colouring wall papers green. It is called Scheele's green. In damp weather persons who live in rooms decorated with such papers are subject to various symptoms of arsenical poisoning, the most obvious of which is a severe irritation of the lining membrane of the nose and eyes. Moreover, green is not the only colour in use that is produced by arsenical compounds.

Besides the masks and respirators which I have mentioned, a great deal may be accomplished in almost all cases by frequent change of air and good ventilation.

There are also a great many manufacturing processes in the working of which organic matters escape into the air in the form of dust For instance, in the spinning of cotton, of wool, and of silk, there is an enormous amount of the fine fibres of these materials given off in the form of dust, and those who work in spinning-mills are subject to lung diseases.

It is difficult to procure good and efficient venti-lation in these rooms, because a considerable amount of -warmth is necessary, and so, as a matter of fact, these places are kept as close as possible.

Offensive organic matters are given off into the atmosphere in many instances, as in gut spinning, bone boiling, tallow melting, etc. It is difficult to show directly that these matters are injurious to health, but, at any rate, they are extremely offensive, and those places in which such processes are conducted could be made much less disagreeable by carrying the fumes given out during the boiling through the furnace, by means of a flue rising from the boiler and connected with the furnace; a practice now very commonly adopted.

Matchmaking, until a comparatively recent date, was attended by a frightful disease which attacked the jaw-bones. This was caused by the particular form of phosphorus which was then used, the form I have shown you several times - vitreous phosphorus. It is very volatile, highly poisonous, rapidly oxidises in air, readily catches fire, and gives off irritating vapours; but hap-pily a form of phosphorus was almost accidentally dis-covered which is comparatively harmless. I told you that there are two forms of oxygen; in the same manner certain other bodies are found in various forms. For instance we find carbon as soot, or as plumbago (black lead), graphite, or as the diamond, and it was discovered that there was also another form of phosphorus which goes by the name of red phosphorus. It is not as volatile or poisonous as the other; it does not combine anything like as readily with oxygen in the air. The introduction of this in the manufacture of matches abolished, practically speaking, the disease to which the makers of matches were formerly subject.

In the manufacture of india-rubber articles a curious substance is used which is called bisulphide of carbon, a combination of carbon and sulphur. It is a beautiful clear yellow liquid of an extremely offensive odour, very volatile, and has the property of dissolving india-rubber.

For a long time india-rubber was comparatively little used, because it was not known how to dissolve it; but when it was discovered that bisulphide of carbon was capable of dissolving it, and then could be evaporated, it was found that articles could be made of any shape or form.

People who work with this substance suffer from the vapour it emits, which is very heavy, and so keeps low down in the room. A great number of india-rubber articles are made by poor people in their own homes, not in manufactories, and when the vapour given off in the process of working this material is breathed it causes various symptoms, as headache, nausea, and convulsions, and in the end paralysis. The way to prevent this is to see that the rooms are well ventilated, and especially that the air of the lower part of the apartment is frequently changed. Fortunately the vapour is a very irritating substance, and so its presence is easily detected.

In the manufactories of chloride of lime (bleaching powder), and in places where it is used for bleaching wool and other materials, chlorine gas is given off into the air, and irritates the respiratory passages when breathed, from which we can see that these places should be very thoroughly supplied with fresh air.

A compound of chlorine called hydrochloric acid is given out in large quantities during the preparation of carbonate of soda. Soda is prepared in enormous quantities from sea salt, and the vapour evolved during its manufacture is an extremely irritating gas, which used to be allowed to escape into the air from tall chimneys, but is now, however, absorbed by passing the fumes through condensing towers in which there is coke washed with a stream of water.

During the preparation of sulphuric acid, sulphurous acid gas is set free, but the manufacturer finds it is a.