G1

Ga

G2

geometrical construction. Referred to perpendicular axes, these positions are measured in feet as follows:

Find approximately, by taking first and second differences, the x and y components of the velocity and acceleration of G when in the position G. Find also the resultant velocity and resultant acceleration for this position.

The mass of the balance weight was 351 lbs. Find the magnitude and direction of the force corresponding to the acceleration for the position G. Plot the points on squared paper, and on the diagram exhihit the velocity, acceleration, and force as

vectors.

Attempted by very few candidates, but well answered by those who did attempt it, though in some cases the plotting was unsatisfactory.

HONOURS.

Results 1st Class, 1; 2nd Class, 3; Failed, 18; Total, 22.

Twenty-two candidates entered for this stage, and the work was much more satisfactory than in the preceding year. Questions 61, 62, 63, 66, and 67 were the favourite ones. Most of the answers to Question 61 were very good, the bulk of the candidates selecting division (a), but the sketching in some cases was unsatisfactory, especially with regard to the details of the feed motions. In division (b) the sketching was much better, and the details were much more carefully shown by the candidates who attempted this part of the question. In Question 62 the majority of the candidates selected division (a), but most of those omitted to explain how they would test the accuracy of the instruments employed in the experiment. The answers to Question 63 were on the whole satisfactory, the diagrams were carefully drawn, but many candidates contented themselves with dealing with only one-half of a revolution of the crank, instead of one complete revolution as was asked in the question. Very few candidates attempted Question 64, and only one secured an accurate result. Question 65 was attempted by only a few candidates, but was well answered. In Question 66 most of the incorrect answers were due to faulty arithmetic, candidates showing a sound enough knowledge of the necessary formulæ, but making serious blunders in their calculations. Question 67 was well answered. The remaining four questions, 68-71, were each attempted by only a small number of students. As a rule the work was fairly satisfactory.

། ་

Report on the Examination in Steam.

STAGE 1.

Results 1st Class, 424; 2nd Class, 408; Failed, 496; Total, 1,328.

There were 1,328 candidates in this stage, being a slight increase compared with 1,300 last year.

SKETCHES.

The standard reached in Questions 1 and 2 is now fairly high, and the details shown often exhibit a working knowledge of the subject. Candidates are sometimes handicapped by omitting to provide themselves with compasses and straight-edges, and suffer accordingly. The sketches in Question 3 were not so good, probably because candidates were not asked for 'good sketches' as in the previous questions. On the whole there is no need to complain of the sketching, but it is very necessary that candidates should be kept up to the mark.

CALCULATIONS.

The usual difficulties were noticed as soon as candidates tried to mix the Centigrade and Fahrenheit scales, but this confusion is growing less marked as men get accustomed to the former. The use of the slide rule would save many mistakes and much labour. Several candidates drew attention to the fact that the ruling of the paper into one inch squares was not accurately done. The inch was more accurately 2.5 cm.

Q. 1. Describe, with good sketches, one, and only one, of the following,
(a), (b), (c), or (d) :-

(a) The crank shaft bearing of a horizontal or vertical engine.
(b) The crank axle of an inside cylinder locomotive.

(c) The piston of a gas or petrol engine, showing the packing,
and the pin to which the connecting rod is attached.

(d) The rotating part of a Parsons' or other steam turbine,
showing how the vanes are fixed.

(a) The favourite section of this question, andstudents showed considerable familiarity with the subject.

(b) Fairly often attempted, but many had no notion where the eccentrics were put and a number showed cranks at wrong angles.

(c) Very frequently attempted, and mostly with success. There is evidently much familiarity with the petrol engine.

(d) Not often done, and attempts, when made, often sketchy and showing no familiarity with the matter.

Q. 2. Describe, with good sketches, one, and only one, of the following (a), (b), (c), (d), or (e) :—

(a) A steam stop valve of the screw-down type.

(b) A locomotive regulator valve of any type.

(c) Two forms of boiler stays, stating the use of each.

(d) The front plate of a Lancashire, Cornish, or return tube
marine boiler, showing how the boiler shell is attached.

(e) The carburettor of a petrol or oil engine.

(a) Often well done, but an astonishing number of sketches showed no provision whatever for the removal of the valve or indeed in certain cases for its ever having got there.

(b) A locomotive regulator valve is not an easy thing to sketch and many students got into difficulties and were unable to make their sketches clear.

(c) Usually done well and often attempted. A great proportion of the candidates appear to have worked in a boiler shop.

(d) Not so often tried as the preceding section and not quite so wel. done. The question offered a more promising field to the candidate who had only seen the outside of a boiler in the distance.

(e) A number of excellent answers and equally good sketches.

Q. 3. With a small experimental boiler you are finding the pressure of steam when its temperature is, say, 100° C., 110° C., 120° C., etc. Show, with sketches, exactly how you would proceed. In what way does the presence of air with the steam spoil your results? Often attempted by men who would have left it severely alone had it not been one of the three important questions. Every kind of answer was given. That part of the question relating to the effect of the presence of air was difficult and it was therefore marked leniently. Most of the candidates have evidently never taken part in or even witnessed experiments illustrative of this portion of the subject.

Q. 4. State the following amounts of energy in foot-pounds :(a) A weight of 35 tons may fall vertically 15 feet.

(6) The Kinetic Energy of a projectile of 60 lbs. moving 2,000 feet per second.

(c) The Calorific Energy of 1 lb. of coal, 8,500 Centigrade pound heat units.

(d) 30 lbs. of water raised from 40° F. to 103° F.

(e) One horse-power-hour.

(ƒ) One kilowatt-hour.

(a) Usually correctly done.

(b) The formula was often given wrong either by omitting the figure 2 or by leaving out g.

(e) Often unattempted, but a fair proportion of correct results. The usual contusion between Centigrade and Fahrenheit units was noticed.

(d) The same remarks apply to this as to (c).

(e) The answer to this is virtually given in the table of constants and so there were many correct solutions.

(f) Many failed to work this correctly, putting the 746 in the numerator. In answering Question 4 few of the candidates used logarithms or slide rules; they seem to prefer long methods of multiplication and division.

Q. 5. It used to be thought that by cutting off earlier and earlier in the stroke, we got better and better results. Why is this untrue? It used to be that the slide valve was never found on economical engines; why is it now in use on many large and economical engines?

The reason why the practice of the early cut off could easily be pushed too far was generally understood, but only in a vague manner, and hardly any thoroughly correct answers were given. Why the slide valve is now used on large and economical engines was answered in many ways and not a little ingenuity was shown; the favourite reply was to refer to the introduction of the double ported and balanced valves.

Q. 6. The mean effective pressure on the piston, both in the forward and back strokes, is 62 lbs. per square inch; cylinder, 18 inches diameter; crank, 18 inches long. What is the work done in one revolution?

An easy question and frequently solved correctly. We are glad to think that nearly every candidate who relied upon the P.L.A.N. formula came to grief.

Q. 7. A pound of oil contains 0-85 lb. of carbon and 0-15 lb. of hydrogen. What weight of oxygen is sufficient to produce CO, and H,O by combustion? Take the atomic weights of C, 12; of O, 16; of H, 1. If 1 lb. of oxygen is contained in 435 lbs. of air, how many pounds of air are needed for complete combustion ?

This appeared to be a difficult question, but an astonishingly large number of perfectly correct replies were made. Hardly any who tried it got it wrong. The way in which this question was answered shows wide reading on the part of many works apprentices.

Q. 8. A slide valve is worked directly from an eccentric. The advance is 30°. When the main crank has moved 20° from the line of centres, show the position of the eccentric crank. The half travel being 3 inches, mark off this radius and drop a perpendicular on the line of centres; what have you thus found?"

This was a very easy question, but numbers failed over it; failed where they could probably have worked successfully a much more complicated question on the Zeuner diagram. We think the answers to this question show that the Zeuner diagram is not understood. A number lost marks by drawing a 1 inch radius instead of a 3 inch one, they meant very possibly to be working to half scale, but it was not always possible to know whether this was so or not.

Q. 9. A formula for Regnault's total heat I will be found on the tables supplied to you; it is the total heat which must be given to 1 lb. of water at 0° C. to raise its temperature as water to ° C., and then to convert it all into steam at 9° C. What is the heat which must be given to 1 lb. of water at 40° C. to convert it into steam at 170° C.

Frequently answered correctly, and accurate knowledge upon the subject appears to be increasing. It is worth notice that a very nearly correct answer could be obtained by an entirely wrong method. A good many students subtracted the 40 from the 170 before multiplying by 305, a serious mistake.

Q. 10. A boiler furnace fire is about 12 inches thick. What do we know as to the way in which the combustion is going on at various places in the coal and above it and in the space just on the furnace side of the flues? Take any state you please; just before fresh coal is supplied or after, but you must say what the conditions are.

A number attempted this question only when they found they could do no others, and many rambling replies were therefore sent in. Some thoroughly good answers were given, but chemical knowledge was more often exhibited in Question 7 than in this.

Q. 11. F lb. is the outward radial force on each ball of a governor required to keep it in equilibrium at the distance feet from the axis when not revolving. The following are for the

The weight of each ball being 10 lbs., what is the centrifugal force of each at n revolutions per minute, the radius being r. What are the speeds for the above values of r when the governor is revolving?

This was obviously considered a difficult question and many of those that did attempt it arrived after ingenious struggles at incorrect solutions. The simpler form of the centrifugal force formula appears well known.

Q. 12. In a gas engine cylinder where v2′2 and p

14.72 it was

known that the temperature was 130° C. What is the temperature when p = 122 and v = 1°2 ? .

Frequently answered, but the answer most often given was 587 deg. C., an answer obtained by treating all temperatures as though they were absolute, and even then arithmetical errors were numerous.

Q. 13. The total heat, that is, the heat H required to convert a pound of water at 0° C. into a pound of wet steam at 0° C., having a dryness fraction æ, is

H = 0 + xL

where L is the latent heat of 1 lb, of dry saturated steam. If wet steam 90 per cent. dry (that is, x 09) at 2033 lbs. per square inch, is throttled by passing through a non conducting reducing value to 1019 lbs. per square inch, what is its dryness at the lower pressure? Remember that H is the same for the two kinds of steam; it keeps constant when steam is, throttled.

This was looked upon as a difficult question, and therefore nearly xclusively attempted by candidates who knew they could do it. A few brought in the pressure as a multiplier.

STAGE 2.

Results: 1st Class, 268; 2nd Class, 520; Failed, 323; Total, 1,111.

In this stage there was a considerable increase in the number of candidates, the actual figures for this and last year being 1,111 and 940 respectively.

There is very little ground for complaint as to the quality of the sketches. The remarks made as to Calculations in Stage 1 apply to Stage 2; the Arithmetic is not at all in a satisfactory state.

Q. 21. Describe, with good sketches, one, and only one, of the following, (a), (b), (c), or (d):

(a) The crank shaft bearing of a horizontal or a vertical engine stating the diameter of the bearing.

(b) The crank axle of an inside cylinder locomotive, inserting approximate dimensions.

(c) The piston of a gas or a petrol engine, showing the packing, and the pin to which the connecting rod is attached. State the diameter of the piston.

(d) The rotating part of a Parsons' or other steam turbine, showing how the vanes are fixed.

(a) This and section (c) proved to be the most popular parts of the question. The crank shaft bearing was as a rule well sketched and described, very much more information was shown than in the corre sponding question in Stage 1, even when allowance is made for the difference in standard.

(b) Popular and generally well done.

(c) Very popular and rarely badly done. The facts about petrol engines are well known.