ANSWERS TO QUERIES.
If you've noticed an error in this article please click here to report it so we can fix it.
Oar readers will be informed by the Editor.on any points connected with the construction or use of commercial motors. Where a direct reply is desired, a stamecd addressed envelope should be enclosed : if a request for , privacy is not specially made, any query and answer may be published:
Petrol Tax Rebate.
 (Suffolk).—Free of duty refers to the supertax of 6d. per gallon, which is paid in advance by holders of ordinary " full-duty " licences when they apply for that licence. As you have not paid this, you are obviously not entitled to any return in respect of it. The rebate which the Inland Revenue officer has offered you is one half of the Inland Revenue tax of.s6d. per gallon', which you pay in the purchase price of the petrol. He is quite correct in his statement.
Licence -for Steam Wagon Driver's Mate.
 (Liverpool).—The second man on any steam wagon is not required to have a licence, unless he performs some of the functions of controlling the vehicle, i.e., steering, braking, regulating engine power, or manipulating change-speed gear. He can stoke and feed the bbiler with water, and lubricate the engine, but if he performs any of the functions mentioned he mint hold a -licence.
It is not necessary for the second man on a petrol wagon to be able to drive or to hold a licence ; but he must not touch the controls, otherwise he renders himself liable to prosecution.
Steam Wagon Boiler Trouble.
 (Manchester).—The boiler is evidently in a dirty condition, which is proved by it being difficult to keep up steam. It aught to be wished out more often. The leakage at the rivet heads also indicates corrosion at the seams.
There are varicus compounds on the market for using in steam boilers, sts213. as Boilerine, marketed by Boilerine, Ltd., Old Kent Road, S.E., or Litholine, supplied by the Litholine Co., Cromwell Buildings, Manchester. These compounds are prepared after analysis of the feed water, and full instructions are given.
Contracting for Ploughing.
•  (Whalley Range).—There are a few people who are buying tractors with the idea of contracting for ploughing and other operations. You are hardly likely to make much money out of it until you come to the autumn ploughing season, when, of course, you will be able to get plenty of work more or less at your own price, as farmers then will all want their work do.ne at once. If you do establish yourself as a contractor, representations will have to be made to Mr. Brothero's department to see that you do not get unfair competition through the Government contractors.
It is very difficult to advise you as to the exact ma-. chine to select, so much depends on the kind of ground which you are going to work. There are several British tractors of sound design on "the market, one or more of which should meet your particular requirements.
Buying a Steamer..
 (Ross).—To give you tips for the running of a steam wagon, in the course of a letter, is, we are afraid, out of the question. We suggest that you refer to our back numbers, in which we gave a series of articles entitled "Keep your lorry fit." We have also, as you may have noticed, recently published a series of articles dealing with the selection and upkeep of steam wagons in general. As regards coot of running, a 6-ton steamer on steel tyres, running about 200 miles per week, would B46 cost is. 3d. per mile. If the mileage per week were less, the cost per mile would increase slightly owing to the effect of the standing chargns. If a trailer is used, the total load moved would be nine tons, and the cost per mile would then be Is. 4id.
Our advice is, if you are thinking of purchasing a Sentinel, to have a rubber-tyred one. With rubber tyros there is less wear and tear on the mechanism,' and the average speed of running is greatly increased.. The vehicle would have to be registered at your.local. police station, at a cost of £1. Insurance will be about £40. In this matter you should get into touch with one or other of the following companies :—Car and General Insurance Corporation, Ltd., 83, Pall Mall, London, S.W. 1; British Dreadnought Underwriters,Ltd., 14, Cornhill; London, E. Q; ; the White Cross Insurance Association, Ltd., 5, Moorgate 'Street, London, E.C. 2.
The driver's and steersman's licences (the latter is technically unrequired, but is actually insisted on by most magistrates) are 5s. each and are also obtainable at the local police station.
Cylinder-head Gasket Wanted.
 (Royston).—The only agent for Beaver engines in this country is S. Smith and Sons. You will, however, find Halite to be quite a satisfactory jointing for your purpose. The writer has actually made satisfactory cylinder-head gaskets from brown paper, soaked in boiled linseed oil. If you write to Wood-Milne, Ltd., at 21, Albion Street, Gaythorn, Manchester, we have no doubt that they will be quite pleased to give you the names of their agents who stock the jointing material which you have in mind. They would also advise you as to its suitability for the purpose you name.
Gas and Petrol Equivalent.
 (Peckham).—The total cost of running a twoton van, including the necessary allowances for interest on first cost, depreciation, insurance, wages of
driver, fuel and oil, etc., is 10d. per mile. This includes petrol at the net price of 3s. 3d. per gallon (3s. 6d. per gallon, less the rebate of 3d., half the Inland Revenue tax), and.is calculated on a basis of 400 miles per week running. Presuming that you can obtain coal-gas at 4c1. per 100 cubic ft., and that you can run, as you should, 12 miles per gallon on petrol, and the same distance on 250 cubic ft. of gas, the saving by the use of gas would be 2.42d. per mile, reducing the overall costs to 7.58d. per mile.
Gas Bag Filling.
 (Bristol).—In the branch pipe which feeds the engine from the gas hag (that is, when the same pipe is used for filling the gas hag and a branch is taken from it to feed the engine) there should be a shut-off
valve which entirely -closes the orifice. This pipe, which acts as the feed pipe to the gas. bag, should end in a 2-in, external-threaded union to engage with the internal-threaded flat-faced union on the cormection pipe which comes from the meter.
. The shut-off valve should either take the form of a plug cock or a disc valve which would open under pressure from the meter and close under pressure from the gas bag when the connection tothe meter is disconnected. For a 2-in. pipe the plug cock is best, as it gives a clear gasway.You will see that this saves any blank cap. It is always better to have some simple back valve in the gas supply to the engine, as you want to avoid any risk arising from popping back.