The study of tuberculosis and medical education in connexion with it received a great impetus from several directions. The Phipps Institute at Philadelphia was established at the opening of the decade; a tuberculosis research laboratory at Johns Hopkins University in 1916; and one in connexion with the National Jewish Hospital for Consumptives at Denver in 1918. Edward L. Trudeau, the recognized pioneer and leader of tuberculosis activities in the United States, died in 1915. During the last year of his life there was planned the Trudeau School of Tuberculosis, the first of its kind, to give systematic instruction to physicians. This held its first session at Saranac Lake, N.Y., in 1916, and was so successful that several others were established in other parts of the country. As a memorial to Trudeau, funds were raised to establish the Edward L. Trudeau Foundation, which aims to carry on research work and the Trudeau School and assist in the administration of the Trudeau Sanatorium. In 1916 The American Review of Tuberculosis, a monthly scientific periodical, was founded by the National Tuberculosis Association. It was in 1921 the only tuberculosis journal in the Tin ted States and had done much to stimulate the study and investigation of the subject.
Perhaps the most significant and unique achievement of the period was the Framingham (Mass.) Health and Tuberculosis Dem- onstration. Supported by the Metropolitan Life Insurance Com- pany and the National Tuberculosis Association, this agency under- took a tuberculosis survey of a community of 15,000 people, to intend through six years. The work began in 1916. By 1920 the greater part of the population had been studied in its medical, eco- nomic and sociological relations. The survey established many facts, which seemed likely to serve as important data upon which future campaigns against tuberculosis might be based. Between 1916 and 1920 the tuberculosis death-rate of the community fell from 121-5 to 64-5 per 100,000. At the same time it was shown that the ratio of active cases to deaths was 9 or 10 to I, instead of 3 to I, the ratio which records of the community had previously shown. The survey supplied standards of diagnosis and treatment, of case detection, of school, factory and home control, of necessary expenditures against tuberculosis, etc., which promised to be of service not only to the whole nation but to the world at large.
(A. K. K.)
TUNISIA (see 27.393). The pop., according to the 1911 census, consisted of 1,739,744 natives; 11,300 Maltese and 50,477 Jews. There are but few Arabs, the majority of the population being I \rabic-speaking Mussulman Berbers. The chief feature of the . European population is the presence of large numbers of Italians, . ,vho compete with the French in influence, and who have certain privileges with regard to language and education. According the 1921 census the European pop. amounted to 156,125, of , vhom 54,477 were French, 84,819 Italian, and 13,509 Maltese.
These figures show an increase of 8,000 in the French inhabitants ince the census of 1911, and augur well for the further develop- ncnt of French immigration to the protectorate.
j Since 1905 Tunis has had a Consulting Conference formed by .5 French members chosen by universal suffrage, and 16 natives, ne of whom is Jewish, nominated from among the notables by he Government. This body expresses its views on all financial
, natters of interest to Tunis, whenever any fresh reforms place urther burdens on the country.
c The country is essentially agricultural, and cereals are raised on a in, scale. In 1919, 514,861 hectares were under wheat, and pro-
' uced 1,450,000 quintals. Vines are grown intensively over 23,246
"ectares, and in 1919, 444,157 hectolitres of wine were produced.
i>live trees cover a section of the country, and produced 191,836 uintals in 1919. The export of olives has a promising future. Fish- ig and the sponge industry occupy quite a number of the population, ron and zinc are another resource, 360,453 tons of iron were extracted
1 1919, their value being 14,500,000 francs. The chief mineral realth of the protectorate lies in the immense phosphate deposits,
hich are worked on a big scale. In 1919, 815,385 tons were ex-
| 'acted, of a value of 36,692,325 francs ; this is a considerable drop, for
i 1915 the tonnage figure was 1,075,214 tons. There are valuable
uarries and mineral springs. General trade in 1919 amounted to
^7,789,000 francs, of which 285,761,000 francs represented imports.
- 'he share of France in the imports was 92,309,893 and of Great
,'ritain 67,106,084 francs. Of the exports France absorbed 129,932,-
X>, and Great Britain 15,670,000. In 1918 the total general trade
mounted to 436,990,000 francs, 207,442,000 francs of which were
nports. In the last normal year before the World War, the figure
as 322,918,000, of which 144,256,000 francs were imports.
TUPPER, SIR CHARLES, BART. (1821-1915), Canadian statesman (see 27.410), died Oct. 30 1915.
TURBINES, STEAM (see 25.823 and 842). The progress of ie steam turbine during 1910-21 was very marked both as regards size and efficiency. The pure Curtis type, in which velocity compounding exists at every pressure stage, has been abandoned, except possibly for very small powers, and the design of impulse turbines now follows generally along the lines first laid down by Rateau, and developed principally by Rateau and Zoelly. A single Curtis wheel is frequently used to absorb the velocity due to the expansion of the steam in the first stage, as this practice permits of a greater heat drop in that stage, so that the pressure and superheat are considerably reduced before the steam is admitted to the body of the turbine. Velocity compounding is recognized as less efficient than the abstraction of the energy of the steam by single impulse blading, but the practical advantage of obtaining a large heat drop in the first stage is often considered to outweigh a slight loss of efficiency. The typical impulse turbine of to-day consists of a horizontal shaft carrying a number of disc wheels, each furnished with a single row of blades around its circumference, and running in its own separate compartment. The diaphragms which separate the compartments contain nozzles which are so proportioned that the steam expanding in them from the pressure which exists in one compartment to that in the next acquires just the velocity which can be efficiently absorbed by the wheel in the second compartment. The description later of a modern impulse turbine will make clear its construction and principles of action.
The reaction machine still maintains its position as regards efficiency and, like the impulse machine, is employed for very large powers. In modern machines, although the thermodynamic principles are identical with those of the earlier machines, there has been a considerable change in details of construction. The modern reaction turbine is frequently fitted with a velocity compounded impulse wheel, upon which the steam acts before passing to the reaction blading, the reason for this being the advantage of reducing the temperature and pressure of the steam before it is admitted to the body casing. It is not unusual to design the impulse wheel so that it absorbs about one quarter of the available energy of the steam, with the result that the drum may be materially shortened, the number of rows of reaction blading greatly reduced, and the cost of the turbine lessened. Other features which are. typical of modern reaction machines are the great care taken to eliminate causes of distortion in the casing, by avoiding ports and irregularities of the metal. The casing is always made as symmetrical as possible.
The Reaction Steam Turbine. Enormous progress has been made with the reaction turbine invented by Sir Charles Parsons, both as regards size and efficiency, and corresponding mechanical developments have taken place in the design. Land turbines of more than about 10,000 K.W. capacity are usually constructed in two or more parts, each part being a complete turbine, but utilizing only a portion of the total pressure drop of the steam. Sometimes the parts are placed side by side, each driving an independent electric generator, but otherwise they are arranged in tandem on a continuation of the same shaft.
This latter arrangement is illustrated in fig. I, which shows a section through a large modern two-cylinder machine constructed by Messrs. C. A. Parsons & Co. Ltd. The steam passes from left to right through the blading of the high-pressure cylinder, and is then conducted by means of the circular external pipe to the centre of the low-pressure cylinder. Here it divides, flowing axially in each direction through the blading to the exhaust branches whence it passes to the condenser beneath. The low-pressure cylinder is built on the " double flow " principle in order to avoid the exces- sive length of blades and size of exhaust branch which would other- wise be required. In turbines of the reaction type there is a differ- ence of pressure between the two sides of every row of blades, and there is thus a corresponding tendency for the steam to leak past the row without passing through the blading. This leakage was a source of considerable inefficiency, and to minimize it, the custom was to employ the smallest practicable radial clearance between the tips of the blading and the opposing surface of the drum or casing. These fine clearances were a source of weakness, as in the event of a slight distortion of the parts by straining or uneven heating, or in case of vibration occurring, there was always a chance of contact occurring, and the danger of this resulting in a stripping of the blades. In order to avoid the fine radial clearances with their attendant danger, Messrs. Parsons introduced the system of end- tightened blading, which now represents their standard practice for the high-pressure end of the turbine where the density of the steam makes fine clearances essential. This is illustrated in fig. 2.
