CHEMICAL DRAWING EDWARD M. HOSHALL 2434 Guilford Avenue, Baltimore, Maryland
The publication of chemical articles frequently requires the aid of sketches, drawings, diagrams, and cumes. T o the author these are usually a source of dificulty, and to the editor a source of inconwenience, in that drawings must frequently be redrawn by the author,
or a draftsman must be employed. It i s the purfiose of this @per to present a brief course in "Chemical Drawing," based on simplified pinriples of mechanical drawing, together with certain mggested conventions which confmm to standard practice in leading chemical pnblications.
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him; he must rely on lines and outlines to convey the thought underlying the sketch. The bare outline must often be supplemented by information regarding details, such as scales, dimensions, legends, and, in drawings intended for publication, reference to the text. This type of technical drawing, including the use of certain conventional representations considered good practice as applied to chemical problems, will be designated as "chemical drawing." Especial attention will be paid to drawings of this type intended for reproduction.
RAWING has been the universal language from the cave-wall carvings of the Pliocene period to the highly technical scientificdrawings of our own machine era. Modern scientific drawing is the technical language of those engaged in the respective sciences: an expression and a record of ideas and information for the execution of designs. In preparing such drawings the draftsman is confronted by a diflicult task. He cannot, like the artist, employ light, shade and color, to aid
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Fundamentats of Chemical Drawing
It is not the intention to present in this section an elementary course in mechanical or engineering drawing, for many excellent books on these subjects are available. The prospective student and others interested are referred to the group of selected references which appears a t the end of Part 11. It is suggested that standard texts be used as guides in acquiring a knowledge of general principles. Supplementary notes and observations pertaining especially to chemical drawings for use in publications are offered here. EQUIPMENT
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A set of drawing instruments should include: a ruling pen; a small bow compass with pencil, pen, and divider attachments; a six-inch compass with pen, pencil, and divider attachments, and lengthening bar. In addition, the following are necessary: Drawing board T-square 45 degree and 30-60 degree triangles ~ r e n c hcurves Lettering pens Pencil sharpener Protractor Erasing shield
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12" scale Centimeter scale Thumb tacks
SCALE AND SIZE OF DRAWING
When practicable, chemical drawings should be made to scale. It is obvious that an extensive set-up of apparatus would not be drawn to exact scale, while a working drawing for a piece of glass'apparatus would be. In the majority of cases chemical drawings will be made with their component parts in proportion to each other, but not necessarily to scale. A word may be said regarding the size of the completed drawing. A large drawing is usually more easily exedted than a small one, and on reproduction for publication, defects will be "smoothed over" by using a large reduction ratio. For general purposes it is considered good practice to make the finished line drawing two or three times the size of the desired cut. It may be noted that on drawings for reproduction, any irregdarities may be corrected by painting out the error with white paint or, if it is de8red to shift lines or figures, they may be inked on a separate piece of paper and pasted in the corrected position. APPLIED GEOMETRY AND SELECTION OF VIEWS
Erasers Drawing ink Pencils (2H and 6H) Drawing paper (for I'e of pens)
A fair knowledge of geometry is a requisite if the draftsman is to do more than copy drawings or sketches. The generally useful theorems such as dividing a line, circumscribing, and constructing the common geometrical shapes, both plane and solid, should be reThe use of instruments is fully covered by standard viewed or reference should be made to a standard text. The general principles of orthographic projection texts. 21
apply to chemical drawing as well as to mechanical drawing, except in the number of views required to illustrate an object. In chemical drawing, as a rule one or, a t most, two views will be sufficientto indicate the lay-out of apparatus. The plan view (from above or the top), or the front view, are those in general use. When it is desired to show more clearly the interior construction of an object a view is made "in section." That is, part of the object is cut away and the interior is visible. The surfaces cut from the object by the cutting plane and represented by the sectional view must be "section-lined" or "cross-hatched," to indicate that they are not actual surfaces of the object. The material of which the part is formed may be indicated by the type of section-lining used. Standard sectionliming or cross hatching will be considered in Part 11. Section views are nsed to a large extent in drawings for publication, since the number of views is decreased and the material of construction can be indicated. Another type of view frequently used is the isometric drawing. This is an attempt to combine the pictorial effect of the artist's view with the mechanical view, including the ability to measure the lines of the drawing correctly. Isometric drawing is difficult if the object is complex or is composed of curves and w e d surfaces. However, it presents the picture of an object more effectively than does the ordinary lime drawing.
designation of parts, the legends, titles, and notes. This lettering is shown in Figure 2. I t should be the general policy, in chemical drawings, A to limit the lettering to reference letters or ' numerals, and to instances LM O where the accompanying text cannot Q treat the desired information necessary. The indiscriminate use of lettering. I 3 which could be replaced by printing, 890. is not only a waste of time but makes FrGURE for an unfinished appearance. The essentials of lettering should be reproduction. viewed by reference to a standard text.
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F$sdsiz$n 2
DIMENSIONING
The "rules for dimensioning" as found in standard texts apply to the chemical drawing. The units are another proposition. Considerable lack of uniformity exists in the units employed in drawing. The metric system belongs to the chemist; his supplies and equipment are requisitioned and sold by that system, and yet chemical drawings still have dimensions in the English system and, not infrequently, in both systems. Except for working drawings where standard machine parts are used, it is urged that the metric system be used for all dimensions and measurements. SHADING
STRUCTURE OF LINES
A set of conventional symbols covering all the lines needed for different purposes in chemical drawing is given in Figure 1. It is not possible or desirable to
Adjacent parts (alternate popitiono)
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In drawings it is the customary practice to represent the outline by a uniform bold full line. By doublimg the thickness of the line as in shading, it is possible to improve the appearance and legibility of the drawing. Shading is nsed to advantage in technical periodicals where space is limited and the definition of shape is the predominant feature. The theory of shading can be ascertained by reference to a text; it is sufficient to say here that the simple rule of shading the lower and right-hand lines of all views will usually suffice. Line shading is a method of representing the effect of light and shade by ruled lines. It is difficult to execute satisfactorily and is used but little by the average draftsman. It aids definitely, however, in giving the appearance of relief and an effective finish to illustrations. PROCEDURE IN MAKING A DRAWING
Crors-hatching line
Line of motion 2
FIGURE 1 Reduced to '/z original size in reproduction.
set an absolute standard of weight for lines, since variations will occur with different-size drawings; the contrast, however, should be maintained. The visible outline will, as a rule, be between 0.4 mm. and 0.8 mm. in thickness. LETTERING
It is considered good (and standard) practice in chemical drawings to use the lettering known as "bold face, commercial Gothic, vertical single stroke" for the
a. Data. Survey all data available, having informa-tion as complete as possible. Make use of drawings of like nature, photographs, and descriptions. b. Requirements of the Dram'ng. The finished sheet must bear all information required by the drawing, including, of course, references to the text. The snbject must be presented in a form most desirable to its intended users. In chemical drawing for use by publication in periodicals, drawings representing average practice by the chemical draftsman are to be preferred to those of a highly technical nature. 6. Plunning the Drawing. The principal view is selected and the position of the view which conforms to good practice is determined. The dimensions of the
sheet are choosen in conformity with the suggestions previously given. The scale which will best meet the requirements is selected. The general arrangement of the sheet should he ~lannedby freehand drawinr if necessary, sketching with light pencil lines. d . Execution of Drawings. Border lines are seldom used on drawings for technical publications. Light pencil lines are used to "block-out" or locate the views on the sheet, as decided in the planning step. "Finishing" the drawing consists in inking in the picture and dimensions, with 6rm lines of proper structure as previously recommended. The order of inking is most important and is as follows:
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First, ink all solid circles. Second, ink dotted circles and arcs. Third, ink any irregular curved line. Fourth, ink straight full lines in the order: horizontal, vertical, inclined. Fifth, ink straight dotted Lines in the same order. Sixth, ink center lines. Seventh, ink extension and dimension lines. Eighth, ink arrow heads and dimensions.
Ninth, section-line all cut surfaces. Tenth, add letter notes and references. Eleventh, the name and address of the author should be in pencil, on the margin of all sheets,
A word might be added concerning the mailing of drawings. They should never be folded. It is best to cover the inked surfaces with a piece of tissue paper or light tracing paper, sandwich between two layers of heavy cardboard, and mail in a heavy manila euvelope. If the sheet is too large for an envelope use a mailing tube of sufficiently large diameter so that creasing will not result. The ends of the tube should be covered to exclude dirt and moisture. It is not intended that these observations and notes should constitute a complete course in drawing, but with the aid of the selected references and the sections on Conventional Representation, and Arrangement of Drawings, which will follow Part I, the average chemical draftsman should have a clearer insight into the requirements and methods of making acceptable chemical drawings.
11. Conventional Represenfafion of Haterials and Equipment A chemical drawing cannot.effectively accomplish ferent standards are in what is apparently "good its mission unless i t conveys complete information usage," each standard having the backing of an organizaboth as to the form and the materials of construction tion or society. Until a definite, universal set of standof the object. In a broad sense this is true of all tech- ards is formulated and adopted, the best policy lies nical drawings, since the composition is inferred, as iri in using those standards considered good practice as specialized trade drawings, or else use is made of con- found in the leading technical chemical publications. ventional representations or symbols to convey the SECTION-LIN~G information concerning composition. Symbols and When making section views in drawings, a cutting symbolism seem to reek of the past, of alchemy whose many secret symbols and signs can be traced through plane is passed through the object.., The intersected the centuries to their use in a modified form today. surfaces in this sectional view d u s t then be "crossInvestipators of hatched or "section-lined," to inearly c h e m i s t r y dicate that they h a v e unearthed are not actual more than three sllrfaces, but secthousand alchemitions. The matecal symbols which rials of which the now find t h e i r various parts are greatest use in the formed m a y b e design of bookindicated i n a plates. general m a n n e r Our modernby the type of day symbols rep:-. .,.. ......, .,... ....... section-lining resent a n o t h e r FLEXIBLE u s e d . Of t h e s t e p i n convenALUMINUM RUBBER BRICK SAND MATERIAL tions, a n d y e t many v a r i o u s even they are not s t a n d a r d s proentirely satisfacposed, Figure 3 tory chiefly beindicates those in WOOD WOOD CONCRETE GLASS MERCURY cause of the many good p r a c t i c e systems in use. from the viewAn instance of ....,i: p o i n t of t h e thisistobefound MATERIAL chemical draftsin the case of secSCREEN man. Sources of tion-lining for FILLER CORK a d d i t i o n a l seccopper; four difFrcmta 3
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necessary. A stopcock when drawn alone would probably be shown in 'section, but in an apparatus "set-up" it should be indicated by outlime only. Figure 5 shows some selected drawings of chemical glassware which represent good practice. It would be ideal, but obviously impractical, to preFIGURE4 sent a whole series of drawings for use as models. These few, however, will tion-linings are indicated in selected references, p. 27. indicate the general trend to be followed in making satisfactory drawings of chemical glassware. It may LABORATORY GLASSWARE be noted by reference to the above plate how the use The frequency of illustration of chemical glassware, of heavy lines in the outline emphasizes the object. whether in the laboratory notebook or the patent office The weight of the lines used drawing, suggests the importance of this phase of drafts- in the volumetric flask and the 1. manship. The multiplicity of illustrations of chemical Florence flask is probably the 2. glassware in apparatus catalogs, texts, and publications most satisfactory for general 1 - 1 leaves little to be desired in the way of models to fol- use. - 3. low. The plane lime drawings required are simply exeAnother incidental point I cuted, and yet glaring errors in depiction of the simplest may be mentioned in connec1 4 : 1 apparatus can be found by a perusal of our chemical tion with the drafting of rubFIGURE6 publications. Figure 4 shows four drawings of an ber, glass, and metallic tubing. Erlenmeyer flask; the first three might be termed Figure 6 indicates a few ex"variations," and the fourth accepted as a fair model. amples. No. 1 is satisfactory for representation'of The model is about the most easily draftable which rubber or metallic tubing, using, of course, the appresents a good picture of the object. Simplicity propriate section-lining. Nos. 2 and 3 are not conshould be the keynote in most cases, the object being sidered good practice in indicating glass tubing, No. presented in outline alone, and details used only when 4 being the preferred method. It will be noted in
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Ammeter Voltmeter Galvanometer wattmeter watt-hourmeter Ohmmeter Frequency meter Asymmetric cell Rheostat Condenser Variable condenser Battery
Variable Inductance lnducfive resistance Shunt Transformer Shunt motor series generator Compound motor 3-Phare induction motor Single-phase alternator 3-Phase alternator Synchronous converter Auto-transformer crossing and joined wires Double~poleringle-throw switch Variable resistance Resistance Nan-inductive redstance Motor generator Buzzer 2-Element vacuum tube %-Elementvacuum tube 4-Element (shielded grid) tube A. c. heater type detector No filament rectifier Glow lamp Photoelectric d l Pull-wave filament rectifier Ear-phone% Transmitter Rectifier circuit brealrer Are-light Circuit brealer, two-pole Rotary sp'ak-gap Spark-gap Quenched spark-gap Horn-gap
counterpoise lncandeseent lights Ground Anten"=
No. 4 that the vertical line indicating the end of the tube is lighter in weight than the horizontal lines which refer to thickness of walls of the tubing. I t is obvious that such comments could be extended but the few points brought to attention should indicate that regard to detail is necessary and is the criterion
in general practice. Supplementary symbols may be found in sources indicated in selected references, p. 27. MACHINE PARTS
This section is designed to aid the chemical draftsman who is not familiar with the general principles and prac-
Eye bolt Stove bolt Standard hexagonal bolt and nut Set screw Machine screw Full head rivet (one side Bat) conicat rivet (one side chipped and countersunk) Helical spring spring (simple form) Pulley Solid round bar, conventional "brea!d' Hollow round bar, conventional "brealr" Rectangular bar. conventional " b r e w Wood Pipe elbow (screw) Pipe elbow (flanged) pipe tee (rcrew) Pipe union Pipe coupling Pip= strainer pipe salve (screw) Pipe relief valve Pipe check valve Drilled hole Tapped hole
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covntersunlr hole Sdc Wocd serew Rovnd head wood screw Nail Tack Rope Chain
that distinguishes between the draftsman and the "sketcher" in chemical drawings. ELECTRICAL APPARATUS
The ever-inaeasing number of electrical applications to chemical problems, such as potentiometric and conductimetric titrations, photoelectric colorimetry, electroanalysis, all require that the chemical draftsman be conversant with methods of representation of the apparatus and equipment used. In most cases the draftsman represents electrical apparatus symbolically. The complexity and difficultyof drawing the apparatus itself is eliminated by the use of satisfactory symbols. The symbols in Figure 7 are those occurring most frequently
tice of graphic representation of machine parts-a study which is usually made only by the mechanical draftsman. In working drawings a symbolic representation of standard machine parts such as screws, bolts, springs, valves, nails, etc., may simplify the drawing and still present the necessary comprehensive information. These approximate representations conform to no definite standard, each drafting body setting up its own standards. Figure 8 shows a collection of the more frequently used symbols of machine parts, all of which are reasonably well established as "standards" in the drawing profession. A more detailed and comprehensive study of this subject may be found in the literature.
JANUARY,
1934 SELECTED REFERENCES
Section-lining
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(1) TOWNSEND,C. E. m CLR~~RY. S. F., "Introductm mechanical drawing." John Wiley & Sons. Inc., New York City. 1930,302 pp. (2) FRENCH,T. E., "A manual of engineering draweg,'' 4th ed., MDGraw-Hill Book Co., Inc., New York Clty, 1929, 466 pp.
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(3) SVENSEN,C. L., "The art of lettering," The D. Van Nostrand Co.,New York City, 1927. 136 pp. (4) FR~NcH,T. E. AND MBIKLEJOHN, "Essentials of lettermg," McGraw-Hill B w k Co.. Inc., New York City, 94 PP.
A p W Geometry
(7) United States Dept. of Commerce Patent Office, "Rules of mactice in the United States Patent Office." 1931. p. 55. (8) See ref. (1). p. 101. (9) See ref. (2). p. 448.
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Smbolr. Electrical (10) BISHOP,C. C.. "Electrical drafting and design," McGrawH i l l Book Co., Inc., New York City, 1931, pp. 174-7. (11) See ref. (2), p. 448. (12) See ref. (7), p. 56.
S w h o l s . Machine Parts
(13) HOPPMANN AND S c r ~ r o "Elements , of machine design." Ginn & Co.. Boston, 1928, 327 pp. (5) S M ~ H W.. G.. "Practical descriptive geometrp," McGraw(14) KIMBALLAND BARR, "Elements of machine design," Hill B w k Co., Inc.. New York City. 1925, 281 pp. Tohn Wilev & Sons, Inc., N e v York City, 1923, 446 (6) HOOD. G. J., "Geometry of engineering drawing," PP. McGraw-Hill B w k Co., Inc.. New York City. 1926, (15) See ref. (2), Chap. XI. 290 DD. The second inrtdment of this series of articles will &al with?he gntna2 errangmcnt of drawinp, including detail drawing and lhc jinsshcd sketch.)
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