There are a large number of trades in which solid particles and offensive gases are given out into the air.

For instance, in the air of mines there is a large quantity of finely divided solid particles which get into the lungs of the miners and set up irritation there, often resulting in consumption; and consequently among men who work in mines there is a large death-rate from that disease, because consumption, in manhood especially, attacks the lungs.

It has been ascertained that the death-rate from consumption among miners who work in mines in which the air is changed rapidly, is very much less than among miners who work in mines that are badly ventilated.

In potteries, china works, pearl button manufactories, glass polishing, and cement works, there is a large amount of foreign mineral matter in the air, and the workpeople in them suffer from a high death-rate; this high rate of mortality might be lessened if the solid particles were prevented from getting into the lungs of the workmen, and if these workmen could be persuaded to wear some kind of mask or respirator, by means of which they could breathe and, while breathing, filter the air and separate the solid particles from it, the deathrate from lung diseases and consumption would be considerably diminished. But there is much difficulty in inducing workmen to adopt any such measures; they cannot see that they are for their benefit.

Then, again, workers in iron, and especially in steel, are exposed to the influence.of fine particles getting into the air. These might easily be separated by wearing a kind of magnetic mask which has been devised, through which they could breathe, but which would collect the minute particles and prevent them getting into the lungs.

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, eta, 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 ventilation 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 happily a form of phosphorus was almost accidentally discovered which is comparatively harmless. I told you that there are two formsB 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.