Chemical Drawing 111.
Arrangement
of
Drawings
EDWARD M. HOSHALL 1311 Park Avenue, Baltimore. Maryland
T
HE GENERAL TERM, chemical drawing, would normally include all types of engineering drawings the chemist would be called upon to execute. Drawings required by chemical engineers, however, would involve the study and knowledge of mechanical and structural engineering; subjects which, in so far as 1-d. E w . Chcm.. Anolyl. 6 drawings are concerned, are beyond the scope of this article. I n a restricted sense then, the chemist may look on chemical drawing as covering essentiaUy sketches of apparatus and equipment, ranging from The first portion of this paper will deal with detail the individual units to the assembled apparatus or, as drawings and assembly drawings, while the second part will cover assembly working drawings and detail it is more commonly called, the "set-up." A consideration of arrangement of drawings will working drawings. necessarily include logical methods of indicating units DETAIL DRAWINGS in their relationship to other units, their connections, When i t is desired to convey information concerning proportionate sizes, and also their dimensions, titles, references and other notes which may be required. a single unit, or part of a nnit, and to indicate its form, dimensions, and materials of construction, a separate drawing is made. This is termed a "detail drawing." If the detail drawing is to convey su5cient dimensional and other information for the production of the part or unit depicted, the drawing is then termed a "detail working drawing." A detail drawing is frequently used to stress the more important parts, or &tails, of apparatus. An example of this type of drawing is seen in Figure 9. Figure 10 is a sketch of the apparatus as a w h o l e a n " assembly drawing." In the detail drawing are indicated the approximate size, the shape, the nature of the material, and the necessary references; all requisite to convey the essential information. Another example of a detail drawing is Figure 11. Here, the apparatus as a whole is not shown, but a chemist's knowledge would suggest a distillation flask, a jacketed condenser, a receiver, and a thermometer to complete the drawing. For purposes of emphasis, and to show the construction of details which would have been unstressed in an assembly drawing, this aetail drawing was made. The general conformity to satisfactory conventions, the neatness, and wellbalanced arrangement of this sketch should be noted. Figures 12 and 13 show, respectively, an assembly drawing and a detail drawing of a device for delivering liquid a t constant temperature. The gas-regulator drawn in detail might have yielded more information had the mercury been indicated in conventional manner; also, the rubber tubing might well have been indicated. The general arrangement of the assembly drawing, excepting the ~ e k e r b u r n e r s ,is satisfactory, but the evidence of careful workmanship is lacking. 154
+
Gas
Use may be made of detail drawings to supplement photographs of apparatus , or assembly drawings executed in outline form only, presenting thus a succinct picture of the whole layout with a minimum of work.
The various combinations of units or parts which t h e chemical draftsman may be called upon to sketcharenumerous. To the end that he may be able to execute assembly drawings satisfactorily, i t behooves him to study drawings considered "good practice," to observe the vqious conventions and other "short-cuts" used, to observe scales, noting especially the proportions of various units, and finally to observe the general arrangement of the drawing. The latter precept apparently is often a matter of casual concern, but, nevertheless, aclearcut, satisfactory arrangement can impart more information to the reader than many lines of text. As differentiated from detail drawings already considered, the term, "assembly drawing," is used to designate any sketch which shows the units or parts of an apparatus or machine in their correct relative positions. When it is desired to supply information
necessary for the process of assembling or details of construction, an "assembly working drawing" is made. In these types of drawings i t is necessary to present an easily understood general description of the apparatus as a whole and to describe the relative positions of the various units with su5cient clearness to enable the reader to recognize each part and its mechanical relation to the other parts. In general, it is neither essential nor desirable for assembly drawings to describe every structural feature, since the relative positions of these features can be described more clearly by excluding irrelevant information. Several examples of assembly drawings and assembly working drawings will be considered, and their particular idiosyncrasies and merits, or demerits, brought to attention. The illustrative drawings reproduced have for the most part been abstracted from various chemical publications and are here presented as specimens, both to indicate that some reforms in chemical drawing are in order and to point out some examples of good practice. An important application of assembly working drawings is to the sketching of specially designed glass apparatus. An example is shown in Figure 14. This is a good specimen of this particular type of drawing, for with .its concise information the glass-blower can readily construct the apparatus. In some cases, when dimensioning glass apparatus, both maximum and minimum dimensions are given, thus: 0.6 mm.4.8 mm., or 0.7 mm.-1.0 mm., in order to allow for the necessary variations encountered when working with glass. The expression of tolerances is also used in machine drawings. In some cases, in assembly.. working drawings of
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FIGURE 14
apparatus "set-ups" of a more or less routine arrangement, only special or particular dimensions are given. Figure 15, an oxidation apparatus, is an example of this type, and also a fine example of good practice in chemical drawing. For the successful presentation of a group of units or parts, the above-defined assembly drawing is used. The underlying principle is to give the reader a clear-cut, .concise indication of just what the author has in mind
CAWURETER
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and wishes to stress, without demanding undue use of imagination on the part of the reader. This may be done by rough diagrams, conventionalized.sketches, or by minutely detailed scale drawings, as the nature of the subject requires. It is poor practice to make unnecessarily elaborate drawings of simple apparatus such as distillation layouts, freezing-point and boiling-point set-ups, chiefly from the standpoint of the labor involved, since the average reader should be at least sufficiently familiar with the general nature of the apparatus that he can conjecture any omitted parts or interpret the various conventions used. This defect is seldom noted; unfortunately, the opposite weakness-that of the "abbreviated or incomplete drawing-is far from rare. This may be due to lack of drawing ability on the part of (he author, or to his failure to realize that suitable illustrations can eliminate the necessity for much tedious textual description.
Figure 16 is a rather forlorn attempt to represent a potentiometer layout. Faulty drafting, carelessness, poor arrangement (note ring-stand suspended in mid-air), and failure to make use of appropriate conventions all contributed to yield a poor drawing. A lecture-table experiment is represented in Figure 17 by a semi-sectional (?) view. A single wire to carry 110 volts A.C. and a filamentless lamp could be erroneously interpreted.. bf the layman from this sketch. The lack of conventional cross-hatching to indicate the rubber stopper and the iron electrodes is to be especially noted, since apparently the sketch is a sectional view, and hatching is required for sections. The curiously curved dotted reference lines are neither effective nor neat. Compare this sketch with that of the rotating tester (Figure 18). In the latter drawing the proportions are satisfactory, the arrangement is good, too much attention has not been paid to in-
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confronts editors of chemical publications; a sound cidentals, satisfactory conventions have been used, idea illustrated by an unsatisfactory drawing. Either and, therefore, the drawing gives sufficient information the article must be refused, an unsatisfactory drawing even for a layman. Figure 19 shows another method of indicating parts; they are; in this case, referred to the text by suitable reference letters. Figures 20 and 21 illustrate, respectively, an airpressure generator viewed from the front, and a like apparatus viewed isometrically. Both could he iinproved by the use of larger vertical reference letters. In Figure 21 we note glass tubing bent to 90-degree angles (the dream of the glass-blower) and the very delicate tubing for the air supply, which is obviously misproportioned. n..ibl. 1Wi.a C.d Another type of drawinz, a diamammatic sketch, is sho& in Figure 22. This type is frequently used to indicate electrical connections and to show the Ind. E d . Chsm., A n o W . Ed. arrangement of commonly FIGURE 22 used apparatuq When unfamiliar apparatus is used, it is better practice to make must be reproduced, or a draftsman must redraw the a finished sketch such as apparatusevident sources of inconvenience, both to the editor and to the author of the article. Figure 23. A useful little piece of apparatus is sketched in Figure 24u, but it is doubtful if its value could he ascertained without reading its full description in the text. A second sketch (Figure 246) has been made which with its references is self-explanatory. The latter was no more d i c u l t to execute and yet its clarity is evident even to a layman. This is a typical exInd. E r g . Ckem., Analyl. Ed. ample of the dilemma which FIGURE 23
The limitations imposed by lack of space make it impossible to multiply examplesof suchneeded g reforms in chemical drawing as are sug3 gested by some of the sketches commented upon, and necessitate omission of many excellent drawings representing that perfection Cham.-~wlyrt which i s termed "good practice." FIGURE 240 In Part I11 an attempt has been made to define the types of commonly used drawings, and to give examples of each, showing how concise and succinct information may be conveyed by the use of a satisfactorily arranged drawing. The outcome of these various comments and suggestions depends upon the reader and his ability to observe
other drawings and form definite opinions of their efficacy in conveying significant information to him. Part IV will deal with various methods of p r e s e n t i n g numerical relationships through the media of charts, graphs, and curves. ACKNOWLEDGMENT
The author desires to express his appreciation to those who gave permission to reproduce their drawings. In some cases, it has been impossible to make contact with the authors of drawings discussed, and it is hoped that these authors will accept the writer's apology for what might appear to be a lack of courtesy. FIG-
24b
