Planting Out

In planting out choose a dull, showery time, if possible; otherwise do it in the evening, and shade during the day until the plants have fairly started, always watering liberally'. Lift and plant the plants with a trowel, and if planted two rows in a trench, place them thus .•..• a foot apart. In watering them during summer, give occasional doses of manure-water, made with guano, at about the rate of half an ounce to the gallon of water, or stable-drainings diluted with five times its bulk of water, or well-diluted sewage, etc.; this will aid its progress greatly.

Earthing Up Or Blanching

This requires to be done early in autumn, four or five weeks before the Celery is wanted for use; but later in autumn more time is required for blanching. Gardeners who have to make the supply stretch over as great a length of time as possible, raise their first batch early in February, and nurse it on in heat in pots or boxes, and by this means have strong plants put out in May; this is ready for blanching by the end of July, and fit for the table by the end of August. Successional sowings are made and treated in the same way, until the main supply is ready. Amateurs generally grow one lot only, and this is raised from plants sown from the middle of March to the middle of April. This will require earthing up partially about the middle of September. In doing so, commence by putting a band of matting round each plant to prevent the earth from reaching the centre of the plants. At the same time, clear away any loose or broken outside stalks, and all suckers; break the soil fine with the spade or fork; and work it in round the plants to the depth of 3 or 4 inches. Give a little dusting of lime to the soil - this will keep worms in check - and always choose a dry time for the operation.

If they be growing well, another and a final earthing up may be given some time in October. If they are in double rows, incline the heads towards the centre, so that the tops may be in one straight line. Leave as many leaves above the soil as possible, to continue the growth of the plants. Bearing this in mind, build the earth up as highly as possible, and make the trench with a sharp apex, beating the sides quite firm and smooth. This will assist in throwing off heavy rain; and it will be well to see that water has no chance of standing in the side trenches from which the earth has been dug. Five or six weeks after the final earthing up, the Celery will be fit for use. During hard frost protect the trenches with mats, or straw and mats. For flavouring soups, etc, the green tops are generally used; and to have a supply all through the spring for this purpose, make a sowing out of doors in May, and transplant in the same way as Lettuce on moderately rich soil - too rich soil causes it to grow rank, and less able to stand severe weather. After it is transplanted it requires nothing in the way of cultivation except water when necessary, and to be kept free from weeds. In winter part of it may be protected with mats or straw, so that it may be easily got when wanted during a storm.

Gardener.

Heating By Hot Water

I have read with very great attention the article upon "Heating by Hot "Water," in the February No. of 'The Gardener.' If any one could invent or discover a method by which the necessity for deep stokeholes could be avoided, he would unquestionably do a service of immense importance to horticulturists and others. But I fear we must look for this somewhere else than in Mr Hammond's paper, which only brings forward the ghost of an "old friend with a new face." I do not know whether Mr Hammond is aware of the fact or not, but would he be surprised to find that the method of setting hot-water pipes, recommended by him as apparently something new and untried, has been familiar to gardeners and hot-water engineers for a generation ! It is not the case that ' engineers and gardeners are agreed upon as being essential to a rapid circulation of the water in pipes" that the boiler should be sunk "below the level of both the flow and return pipes," and giving the pipes "a continuous ascent from the top of the boiler to the furthest points of extension in the building or buildings to be heated." This arrangement of the pipes is often carried out, not because it is considered essential for the rapid circulation of the water, but because, all things considered, it is, in most cases, the best arrangement for other reasons.

I can point to very many apparatus throughout the country where the flow-pipe begins to descend immediately after leaving the boiler, and continues to descend until it enters the bottom of the boiler as a return. But every one who has had experience knows that, although this works fairly well where there is only one, or at most two, houses to heat, it cannot, even were there any advantages to be gained, be carried out in any extensive system. Mr Hammond has no hesitation in saying that "the circulation of the water in the pipes will be as rapid with the bottom of the boiler one foot below the level of the return pipes as it would be supposing the boiler was sunk several feet deeper." If by this he means that it makes no difference to the circulation whether it is 2 feet or 4 feet from the lowest point where the return enters the boiler to the highest point (whether this highest point is at the far end or immediately above the boiler) of the flow-pipe, then I say, that I have no hesitation in stating that Mr Hammond is labouring under a grievous mistake.

Those having practical experience know that, where it is practicable to place the boiler - say 10 or 12 feet below the floor upon which the pipes are laid - there is a very much more rapid circulation than where there is only say 3 feet of difference between the bottom of return and top of flow pipes. This result is what any one acquainted with the motive power at work in a hot-water heating apparatus would expect. Mr Hammond enters into this question; but evidently it is a subject which he has not yet mastered. It seems to me that the "primary reason " he gives " why water circulates or moves in pipes" is just, to put it in plain language, because water is water, a fluid, and not a solid, like iron, stone, lead, or ice. He seems also to be of opinion that one particle of water cannot transmit its heat to an adjoining particle, or, in other words, that water is an absolute "non-conductor." This is an error. Water, as well as all fluids and gases, is not a good conductor; but it would be a serious mistake for any one to run off with the idea that it has no power to transmit any heat by conduction.

It is unnecessary to follow Mr Hammond through his explanations of the principles upon which the water circulates, but to show the utter fallacy of the idea that water circulates as rapidly in an apparatus of (say) 4 feet mean height between its lowest and its highest points, as in one with 10 feet, I will quote the formula of one of the greatest living theoretical engineers, Mr Kinnear Clark, of London, who, in his splendid work, ' A Manual of Rules, Tables, and Data for Mechanical Engineers,' page 485, says, when treating of the circulation of hot water, " The velocity of circulation is that of a falling body, due to the difference of height of two columns of water of equal weights of pressure on the base, and it varies on the square foot of the difference of height. The velocity may be found by the aid of Table, No. 85, page 280. The difference of height is proportional to the difference of volumes, Table No. 109; and if the mean height is increased in the same proportion, the increase will be the height from which the velocity is to be calculated.

For example: let the mean height be 10 feet, and the difference of average temperatures of the two columns 10° F., say between 170° and 180°. The respective volumes are as 1.0269 and 1.031, and 10 feet x 1.031/1.0269 = 10.04 feet. Then 10.04 - 10 = 04 feet the difference of height; and the velocity due to this height is 1.61 feet per second, or 96.6 feet per minute. If the height be 20 feet, the difference is .08 feet, for which the velocity due is 136.20 feet per minute. In practice, of course, the velocities due are not attained, nor, at least in the more complex forms, nearly attained. The actual velocities are in some cases not more than a half, or even a ninth, of the velocities due to gravity." This quotation proves conclusively the great value of having depth of stokehole.

And, moreover, when Mr Hammond speaks of his proposal not being applicable where the pipes have to "cross under outside paths," why does he leave out of consideration inside paths? Is it not a fact that inside paths make the application of the method proposed impracticable as well as outside paths? And is it not a fact that there are only very few places where there are neither outside nor inside paths to contend with in the way of having to cross under them?

This being the case, of what practical value is all Mr Hammond's specious reasoning about the particles of water rolling and tumbling down the inclined plane, like so many boulders tumbling down the "Cumberland Screes?" The great mistake he falls into is in treating the question as one of pure hydraulics, whereas it should be treated as a question of hydrodynamics. I will only notice one other point, and that is about the back motion of the water in the flow-pipe. He makes a great deal of this; but he is again labouring under a very serious mistake in assuming that this motion goes on until all the water in the flow-pipes becomes of equal temperature. Some hot-water engineer seems to have admitted this to Mr Hammond; but it must have been some one who knew very little of what he was talking about. The back-motion in the flow-pipe must immediately cease as soon as the average temperature in the flow-pipe becomes higher than the average temperature in the return. The difference of temperature between the upper part of the flow-pipe and the under part has nothing to do with it, any further than that the upper strata travels faster than the colder under strata.

It is well the question should be discussed; but I fear deep stokeholes are a necessary evil, which must be borne with on account of pathways, smoke-flues, and other causes.

A. D. Makenzie. 2 Grove Terrace, Edinburgh, March 15, 1879.