strongly than other more impure waters. This is due to the fact that the elements of which it is composed are more free to unite with other substances than water which already contains more or less matter of a chemical nature.

Air is composed of oxygen, nitrogen, and a small amount of carbonic-acid gas. The proportions are about one part of oxygen to four parts of nitrogen. Nitrogen is a poisonous element, very destructive to life. Upon the presence of oxygen all combustion and chemical action depends. While nitrogen is destructive of life, oxygen gives life, although the former is necessary to dilute the latter, for otherwise the process of oxidation would be so severe that life could not be maintained.

Other subjects might be taken up to advantage if space allowed, but for lack of that, the author has devoted himself entirely to those subjects which have a more or less practical application in the work of plumbing. Much other material, such as the subject of siphonage, will be found at different points, but which for various reasons are considered under other headings.

CHAPTER XXX

DRAWING FOR THE PLUMBER

It is not the purpose of this chapter to go extensively into the subject, but to give some of the necessary principles which will be of assistance along these lines. While it is not to be expected that the average workman in the plumbing trade is or can become a skilled draughtsman, the requirements of the times certainly demand that the plumber, if he is to make the most of his capabilities, must have a certain practical knowledge of the subject of drawing, as applied to his own trade. It is of inestimable value to the employing plumber and to the foreman on plumbing work, to be able to show intelligibly by means of a pencil sketch, for the benefit of workmen or customers, methods of connections, etc. Furthermore, in many cities of the, country, boards of health now demand sketches of contemplated work, both on new and old construction, to be submitted before issuing a permit to perform the work. Again, in many cities, in order to secure a plumber's license, the applicant must be able to draw the connections for work as indicated by his examiners, and to be able to criticise intelligently drawings of plumbing construction of faulty nature. Journeymen plumbers' unions in many instances also require applicants for admission to pass an examination which includes the making and criticizing of plumbing drawings. These remarks will serve to show some of the reasons why ability to read and make drawings is a necessary part of the plumber's knowledge, and it may be truly stated that the necessity for such knowledge is steadily increasing.

The mechanical, architectural, and engineering draughtsman is compelled to go deeply into the subject, but the rudiments are sufficient as a foundation for the plumber, his greatest difficulty being in executing drawings neatly and in such a manner as to be readily understood.

The plumber really needs to be acquainted with only two views, these being known as the plan view and the elevation.

Experience shows that if he learns to properly distinguish between these two views, the plumber's greatest difficulty as a draughtsman will disappear, and that if he does not thoroughly master this principle, his drawings will in all probability be a confusion of plan and elevation, which it will often be impossible for another person to understand. A perspective view of plumbing connections, which, by the way, is a very difficult drawing to make, should very rarely be used by the plumber, although there is a strong temptation to make use of it.

Every object, if it is to be shown completely by drawings, will require two views, a plan and an elevation, although in showing plumbing work, one view will often, and probably usually show the work with sufficient clearness.

A plan view is a view obtained by looking down upon the object as it stands in its natural position. Thus a cellar plan or floor plan of a house is obtained by viewing the cellar or floor from a point above it. An elevation, on the other hand, is a view obtained by standing away from the object, and looking horizontally at it. Every object such as a house, would have four elevations, front, rear, and two side elevations. For the plumber's use, however, not more than two elevations, front and side, are ever needed, and in a great many cases only one elevation is required by him. He must know what the elevation of the house is, in order to know the distance between floors, the total height, etc., in figuring the amount of piping in vertical lines of pipe. He needs the plan view equally as much, to show him the horizontal lines of piping.

It will be clear then that a full knowledge of the work can be obtained only by means of at least one elevation, and the several plan views of the cellar and floors, and in estimating work, these drawings are always necessary. On the other hand, very often an elevation or a plan, as the case may be, will be sufficient. For instance, in showing the principles of certain work by means of a drawing, very often an elevation will show all that is necessary. The idea of plan and elevation may be seen by reference to Fig. 335.

The first is a perspective view of a piece of pipe, and the other two views are the plan and elevation of the same piece of pipe.

The perspective view gives as much information concerning the object as the plan and elevation combined, that is, it shows the length, shows that it is cylindrical, and also the inside and outside diameters. On the other hand, the elevation shows only length and width, and gives no idea as to whether the object is square or round. In connection with the elevation, the plan is necessary, in order to show that the object is cylindrical instead of square, and

Plan

O

Elevation

Perspective View of Pipe

FIG. 335.-Perspective and Mechanical Views of an Object.

that it is a hollow cylinder and not solid. It may be asked, since the perspective in one view gives the entire information, while in the mechanical drawing two views are needed, why it is not better to use perspective views.

In the first place, it is very much more difficult and takes more time to make the perspective view of this piece of pipe than to make the two mechanical views. In the second place, in making a perspective view of a complicated system of piping and fixtures, the task would become so much more difficult than the making of the mechanical views, that the person not well versed

in such work could not expect to do otherwise than produce a drawing which would be utterly impossible to understand.

Regarding the plan and elevation, it may be stated that if the pipe of Fig. 335 had been a square pipe, the elevation would not have been different, but the plan would have been a hollow square, rather than the circular view shown.

Another point that requires mention is the fact that if the pipe had laid upon its side instead of upon end, when the two views were made, the plan would then have been what the elevation now is, but shown lengthwise or horizontally, instead of vertically. The elevation in. that case would be the same as the plan view now shows. If careful study is given to the foregoing simple principles, the subject of plan and elevation will be fairly well understood.

In looking over sketches drawn by workmen, it is especially noticeable that they invariably confuse plan and elevation in showing fixtures, such as sinks, lavatories, wash trays, water closets, etc. To give them a clearer idea of how these fixtures should be shown, Figs. 336 to 339 are given.

These several views are of common fixtures, and in most cases it is as well to show these simple forms of fixtures in drawings, as to show views of fixtures that are more complicated. For instance, the views shown of the lavatory would be much more easily made than those of many of the fancy, high grade lavatories, and they would show the principles involved fully as well.

One very important fact to be remembered, is that no one mechanical view can show all sides of an object, or give all the information that is to be obtained. It is one of the greatest faults of those who are not conversant with the subject, to endeavor to make a certain view show facts concerning an object which cannot possibly be shown by that view. The result of such attempts is usually a distorted drawing which can only be understood after much study and surmising as to the meaning of the one who made it.

The drawings which the plumber will generally require are made up largely of piping, and experience shows that the plumber in making such drawings will have better results if he will draw single lines for his pipe, instead of double lines, such as are shown