Trichlorethylene.--Three non-fatal cases (two of them rescuers) of unconsciousness produced by trichlorethylene occurred in the painting of a brewing vat with a preparation of enamel.* No instructions had been given on the label on the container in which the enamel was supplied, except that when it was used in vats there should be free ventilation. As the result of correspondence with the manufacturers and sole agents, a special Cautionary Notice is now issued with the enamel.

Rubber Solvents.-The manufacture of crêpe rubber soled shoes, in which the soles are made to adhere to the upper sole by means of rubber solution, has led to the increased use of these solutions. The solvents used in making them include trichlorethylene, carbon tetrachloride, benzene and chloroform. When this industry commenced, it was, speaking generally, a side line in manufacture, and the room or portion of the room set apart was often unsuitable for work which gave rise to fume. Complaint of ill-health, particularly from the use of trichlorethylene, was made, and on inquiry at one factory, symptoms of drowsiness, loss of appetite, and shortness of breath. were found among the workers. The solvent carbon tetrachloride also produced symptoms of drowsiness, headache and slight tremor when used in this way. Dilatation of the pupils was observed in one worker, and the close similarity of this body with chloroform suggests that this was possibly an indication of intoxication. The installation of suitable exhaust ventilation in the first case, and improvement in the design of the ventilation in the second, rendered the conditions of work satisfactory.

Amyl Acetate.-No definite poisoning from amyl acetate has been observed, although its use has considerably increased, chiefly in the manufacture of toe puffs, bronzing of picture frames, and lacquering. Unless localised exhaust ventilation, or good general ventilation, where the former is impracticable, is maintained, the workers suffer from headache, drowsiness, and throat irritation, particularly when first commencing work. No permanent injury to health results from inhalation of this fume.

Cadmium Poisoning.-A rare fatality due to inhalation of the fumes from this metal occurred to the engineer in charge of a paint factory. Usually the firm had received metallic cadmium in the form of sticks of the length of a pencil, but a few months. previously they had received the metal in the form of ingots, which had to be melted down to reduce their size. Instead of carrying out the operation, as should and could have been done, in the foundry, where there was a suitable hood and locally applied exhaust ventilation, the engineer, for reasons unknown, elected to do it in a gas-heated circular crucible in which was a vent-hole unconnected with a flue to the outer air, and situated in an inadequately ventilated lean-to. The operation lasted three

*See Annual Report for 1914, pages 47 and 48.

hours: Two men employed with the engineer became seriously ill, but recovered. The symptoms complained of were:-dryness of the throat, headache, rapid pulse, nausea, and passage of brown coloured urine; feeling of cold was also complained of. These are the symptoms of brassfounder's ague, which are believed to be caused by burning of the metal zinc. Zinc and cadmium both belong to the same group of metals, and of the two, cadmium is regarded as the more toxic. Dr. M. Bronte, who made the post-mortem, found signs in the larynx, trachea and bronchi of congestion, in the stomach and intestine of much congestion due to acute early inflammation; fatty condition of the heart and liver; haemorrhagic inflammation of the spleen, and acute inflammation of the kidneys. He considered death due to fatty degeneration of the heart muscle, accelerated by metallic poisoning. Chemical analysis of the viscera was made by Mr. J. Webster, but he was unable to detect any trace of cadmium. He attributed this to the fact that the patient had lived for four days after inhalation.

Thinking that the size of the particles inhaled might be worth investigating, I collected samples of dust four feet above the crucible for Dr. Middleton's examination. He thus reports his finding :

(1) On compressing the partly opened packet å fine white cloud of dust was thrown into the air, and in the neighbourhood of the cloud an air sample was taken with Owen's apparatus.

The particles on the record, varied in size from the limit of resolution (under 1.9 mm. objective and Zeiss 4 eyepiece) to 2 microns in size. A large proportion were under 1 micron. Many of the particles showed pale green translucent appearance, and others were of a bright yellow colour; some were quite opaque. Counting was rendered difficult by the occurrence of a considerable degree of clumping, and from the presence of a soluble substance which retained moisture and then crystallised out. But for these circumstances, the total count would be higher.

The record of 50 cc. air content showed 3253.5 particles in 1 cc. (control=1,312 particles in 1 cc.).

In a count of 1,080 particles 96 per cent. were under 2 microns; the 4 per cent. over 2 microns included 28 from 2 to 3 microns; 12, 3 to 4 microns; 1=4 microns; 1=5 microns; and 18 microns.

(2) A small quantity of powder sprinkled on a microscope slide and examined with dark ground illumination, No. 2 objective and 4 eyepiece was seen to consist of white amorphous particles occurring in clumps of various size, and with a few small particles, apparently impurity, adhering.

Dust. Dr. Middleton continued his investigations into the dust content of the atmosphere of workplaces,* by assisting the National Council of the Pottery Industry by an examination of the effluents from exhaust installations for flint dust in the manufacture of china, especially with reference to the re-entry of the effluent dust into the workplaces, with consequent danger to the

* See Chapter V. of Annual Report for 1922, "Investigation into the Dust Content of the Atmosphere of Workplaces in the Grinding of Metals and Cleaning of Castings."

health of the workers. He visited 14 factories, and made 25 dust determinations, including controls. The results showed that the amount of flint dust emitted into the general atmosphere from dust exhaust plants varies very widely at the different works. In a few cases the amount of flint dust is negligible, in most of the others the pollution is heavy, and the close proximity of open doors and windows indicates that the danger from re-entry of the dust into the workplaces is a real one. Another serious danger existed in some cases where the settling chamber, placed within the factory, was found in a leaky state, dust being forced from the chamber into the room, owing to the faulty design of the plant and the existence of a positive pressure within the settling chamber. As these dust determinations represent a new development in the method of judging the purity of the air in relation to dust, details of the determinations and Dr. Middleton's commentary on them are given without the protocol. The determinations were made with the Owen's dust counter, which is described in the report referred to on page 75.

It must be stated at once that, in consideration of the terms of reference, the inquiry was directed to ascertain the condition of the effluents as near as possible to the point of discharge into the general atmosphere. It follows that, with the exception of those within workrooms, the atmospheres examined are not strictly such as would be breathed by workers, at least for any length of time, but following the fortuitous and variable effects of dilution by other air currents, it may be presumed that the dust content of atmospheres actually reaching workplaces from these sources would be lower than that represented by the dust counts found on investigation. On the other hand, the air pollution here recorded must be regarded as largely additional to that arising in workplaces directly from manipulative processes, though not entirely so, since the dust counts recorded will have derived something from atmospheric pollution produced otherwise than by the flint exhaust effluents. Since it is impossible to assess the influence of such variable adventitious factors, let it be assumed for the purpose of these notes that the atmospheres investigated are liable to be inhaled by the workers. In two of the records, the dust counts gave slightly over 1,000 particles in 1 cc. In one of these, a small proportion only of the dust appeared to be flint, the remainder being smoke; in this case the atmosphere, as sampled, might be regarded as constituting no substantial danger to health. In the other case, a fallacy arises from the very high velocity of the effluent air, which would interfere with the action of the dust recording instrument.

All the other dust determinations indicate a degree of pollution dangerous to health. Some of these are specially worthy of investigation as failing to control dangerous dust.

Cyclone separators were represented by three records, all of which gave high counts of dangerous flint particles.

In eight settling chambers there was leakage of dust, indicating the existence of a positive pressure within the chamber.

From these investigations the systems of exhaust ventilation appear to fail in all except two cases, and the records obtained from these point to possible fallacies which it would be wrong to ignore. The essential part of the system is the filtering or settling apparatus, for at this point it is the object of the system to precipitate the dust from the air current. The dangerous flint dust is so fine as to be scarcely affected by gravity, but is readily carried by air currents while it remains free. The aim of an exhaust installation should be to bring the fine particles to rest against a fixed surface, or to produce clumping of particles to facilitate precipitation.

I would offer the following observations on mechanical systems of exhaust as applied to flint dust :

(1) The velocity of the air current carrying the flint particles must not be too great on the intake side of the system because :

(a) It increases the volume of air to be got rid of by the outlets which carry off the effluent.

(b) If these are insufficient a positive pressure is created within the system which forces air and suspended dust through chinks in the settling apparatus and militates against the arrest of fine particles.

(2) To be successfully trapped the fine particles must be allowed to come to rest either by :

(a) Interposing a filtering medium, or

(b) So increasing the area of the settling chamber that adhesion to fixed objects will occur or aggregation with other particles and consequent weighting will determine precipitation by eddies and gravity, or

(c) By combining (a) and (b).

(3) The path of the effluent should be sufficient to allow of the removal of all air in the system while maintaining a slight negative pressure within it.

(4) The effluent duct should open either :

(a) At least 20 feet above the nearest window, door or ventilator,

ог

(b) Over a water surface enclosed in a sealed chamber which is ventilated by a duct opening as in (a).

Moisture has the effect of facilitating the adhesion of fine dust particles to each other and to fixed surfaces. If aqueous vapour in the form of a jet of steam were introduced into the system between the intake fan and the settling or filtering chamber, the fall in pressure at this point would facilitate the condensation of moisture on the particles and thereby increase the action of the settling or filtering process.

A further special investigation was made by Dr. Middleton of work at the Refractories Industries in the High Peak district of Derbyshire. The object of the investigation was to ascertain the danger to health of workers in the Industries from exposure to inhalation of silica dust, and especially to compare the risks of working in open sand quarries with those in silica rock quarries :

Fourteen dust determinations were made at the processes in the sand quarries and in the neighbouring brick works. The results indicate that the amount of fine silica dust remaining suspended in the air during work in sand quarries is of such small amount as to cause no substantial risk to the health of the workers. Subsequent processes of manufacture into bricks, however, resemble the corresponding processes found where rock is used. Where sand is used, less dust is produced in the preliminary manipulations of sieving, milling, conveying and mixing and from the total absence, or the very small amount of crushing necessary there is less general atmospheric pollution by dust than where rock breaking and crushing plant is a necessary part of the factory.

Dust determinations taken in open silica rock quarries under conditions comparable to those obtaining in the sand quarries, indicate that the amount of fine silica dust remaining suspended in the atmosphere during such work as shovelling broken rock into trolley tubs is of the order of 3,000 to 4,000 particles in a cubic centimetre-definitely a dangerous atmosphere and containing about ten times the amount of dangerous dust that is found in comparable work in sand quarries.

There is no indication, on microscopic examination, that the shape of the grains of quartz in the material have any bearing on the dangerous character of the dust, as is sometimes alleged. On microscopic examination, the fine silica dust which constitutes the danger is not found to differ materially in form from whatever source it is derived, provided that it is produced by the fracture of crystalline quartz. What is important is the size of the particle and the presence of sufficient moisture, with or without clayey matter, to fix the fine silica particles before they are inhaled. In the natural sand of the so-called pocket clays of Derbyshire, there is a minimum of about 8 per cent. of moisture and a proportion of alumina amounting to about 5 per cent.

A further example of the action of clay in diminishing danger from the inhalation of fine silica dust was found in Scotland where the incidence of silicosis in the Refractories Industries is slight. Microscopic examination of dust records shows that many of the quartz particles are attached to little masses of plastic clay, which tends to produce clumping, thus reducing the number of free particles while increasing the size of the clumps. A record taken at a rock-crushing machine where the dust was visible to the unaided eye, showed only 434 particles in a cubic centimetre, 16 per cent. of which were over two microns in size.

The data from these investigations and others on similar lines show that the higher the proportion of free silica in the raw material the greater is the danger of the production of fine silica dust; and with rocks of high silica content the danger increases more rapidly the higher the percentage of free silica rises.

Pitch Dust.-Dr. Bridge examined 28 workers who showed skin changes as a result of coming into contact with dust containing pitch, which led him to believe that prolonged employment might eventually give rise to more serious results. This examination, though it showed characteristic coppery pigmentation of the skin, folliculitis, and areas approximating to keratosis, did not, except in one instance, reveal any evidence of cell proliferation. The age of the majority of the workers (under 40 years), and the short duration of employment, made one guarded in giving an opinion as to ultimate effects. The firm concerned, recognising the risk which might be incurred from the use of this material, have set about finding a substitute which could be regarded as innocuous.

Chronic Manganese Poisoning.-This now well recognised, though rare, form of poisoning has not been recorded previously in this country, although on the Continent and in America cases have been reported.* In 1922, Dr. J. R. Charles†, Honorary Physician to the Bristol Royal Infirmary recorded three cases. A subsequent case came to the notice of Dr. Bridge, who, on visiting the factory where washed manganese ores are ground, sieved and packed, examined all the workers, finding at least three others whom he considered to be early cases. Some six weeks later these cases came under the care of the local

* Journal of the American Medical Association, Vol. 16, 1913; and Journal of Industrial Hygiene, 1919; page 183.

↑ Journal of Neurology and Psychopathology, Vol. III, No. 11, 1922, page 262.