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laboratories, but which attracts much interest in works practice. The results obtained would indicate the possibility of getting consistent determinations of the volume changes of the hide fibers under conditions closely approximating those in full-scale operations. Conclusions
The plumping of limed hide in tan liquors may be satisfactorily determined by the method of Wilson and Gallun.
1-01. 19, s o . 2
I n any given liquor this plumping is determined by its p H value and the valency of the anions present. The degree of plumping rises with decreasing pH from a minimum at the isoelectric point to a maximum a t about pH 1.8 and then drops rapidly with further lowering of the pH. The maximum plumping for sulfuric acid where the anion is bivalent is about half that for hydrochloric acid with a monovalent anion.
A Study of Gelatin Viscosity and Related Problems‘ By M. Briefer and J. H. Cohen ATLANTICGELATINE CO., W O E U R N , M A S S .
I S C OS1 T Y measure-
Following a discussion of the structure of gelatin, of estimating the performance a study is made of the effect of temperature on the of gelatin in practice would ments of gelatin sohtions are usually made viscosity of gelatin solutions with time of standing. be much simplified. The two under conditions choseneither Consideration is given to the effect of agitation on visf a c t t o r s are, however, funccosity. Solution equilibrium and concentration q u i t i o n s of different physical a t random or for reasons of librium in their relation to viscosity are defined and disproperties, or a t least of difconvenience. Such measurecussed. The several phases of the gel-sol condition are f e r e n t s t a t e s of the same ments are, of course, of local studied in detail. property, according as one value only; they are not cornparable with measurements in Viscosity measurements are made under varying conwishes to choose from among ditions of time, temperature, and concefltration, and the several theories on the other localities and rarely the results are applied to practical viscometry. structure or constitution of with those in the published literature. gelatin jellies. The Edible Gelatine Research Society has developed proA reasonable conception of what takes place during the cedures for both jelly strength and viscosity measurements process of swelling, melting, and setting of gelatin-water in the hope of standardizing the conditions under which the mixtures is quite possible from our present knowledge of work is to be done.2 A standard capillary tube viscometer colloidal behavior, so well advanced by eminent investigators together with a calibration curve for each instrument is of recent years. The miters have therefore discussed available. For jelly strength determinations the Bloom briefly the conditions governing and affecting viscosity and gelqmeter has been adopted. The viscosity measurements outlined their conceptions relative to the structure of gelatin reported and discussed in this PaDer were first undertaken as jellies. a review of the standards proposed by the Edible Gelatine Structure of Gelatin Jellies Research Society. The work has since been expanded, however. It is always interesting to note in what manner the obvious All scientific research must finally be translated into terms facts of natural phenomena of sensible proportions relate of practical value or else remain a laboratory curiosity. to the microscopic divisions of substance. As a general Moreover, i t must be determined in so far as possible to what proposition, aggregates of matter of sensible mass assume extent the results of laboratory experiments are effective in roughly the form and structure of their microcomponents. general practice. For example, i t will be shown that Loeb’s’,* This must proceed from the fact that the physical properties conclusion relating to changes of viscosity with time and of bodies are but multiple effects of the physical properties temperature does not hold for gelatin solutions of appropriate of the units of their composition. Thus, Proctor2 reminds concentrations and temperatures. If this is true, then prac- us that the connective tissue consists of fibers, which in turn tical viscometry requires, and may employ, conditions such are made up of small fibrils of about 1 p in diameter; and that the effects described by Loeb are negligible. B ~ r r e t tfrom , ~ a study of the work of Zsigmondy and others, The viscosity of gelatin solutions is of sufficient importance as well as from his own researches, concludes that the real in manufacture to warrant close attention. The choice structure of gels is a fibrillary network, at first amicroscopic, of time, temperature, and concentration must be such as and later becoming ultra-microscopic, and further that by will best indicate the differences between various grades appropriate experimental conditions it may be made to inand kinds of gelatin. It is obvious, also, that these differ- crease in thickness until a diameter exceeding 1 p has been ences should have as large a value as possible, consistent with reached. Loeb4 has shown that suspensions .of powdered good practice, in order that specimens of nearly equal value gelatin and gelatin in solution (sub-divisions of the larger may be clearly differentiated. aggregates) have reciprocal relations with respect to the If jelly strength and viscosity were interdependent-had influence of eledrolytes on the viscosity and osmotic pressure, some specific numerical ratio one to the other-the problem and it has been shown by one of the writers6 that the plasticity of nitrocellulose skin or film-a plastic solid about 1 Presented under the title “Some Viscosity Measurements of Gelatin” 0.005 inch in cross section-is a linear function of the tembefore the Division of Leather and Gelatin Chemistry at the 72nd Meeting of the American Chemical Society, Philadelphia, Pa., September 5 to 11, perature, closely approximating a curve of the viscosity of 1926. nitrocellulose in solution. SThese methods are stated in a pamphlet issued and freely distributed To whomsoever these conclusions are acceptable it appears by the society t o its members. clear that an identical form and possibly structure persists * Numbers in text refer to bibliography at end of paper.
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February, 1927
alike in the sensible proportions of the fibers of connective tissue or the relatively large particles of powdered gelatin, and the microscopic division of these bodies as they exist in gelatin gels. Mobile liquids a t rest are undoubtedly composed of spherical particles. The components of plastic solids are in all probability of irregular formation or aggregates of distorted spherites. The orientation of large aggregates of these divisions invariably follows the form of their microparticles. Bogue6 conceives of a fibrilla or catenary thread structure for gelatin gels. The improbability of such a structure for gelatin sols is, however, admitted by the same author. Instead, he suggests that gelatin sols consist of slightly hydrated molecules, united in short threads, resembling streptococci. Proctor' assumes an elastic cohesion of jelly, which implies some sort of connective structure and defines the gel form as composed of tenuous and possibly flexible crystals which interlace. These break up on melting into smaller and smaller fragments, and with rising temperature dispersity is increased. Above 70" C. the solution is assumed to become nearly molecular. Bogue's catenary thread theory and Proctor's flexible crystal or net structure for the gel state seem alike within the range of probability. It is not so clear of the conditions postulated for the sol state. The connective tissue of hide pieces is a prolific source of gelatin. When such pieces, previously swollen by appropriate means, are first covered with water in cooking tanks, the mass forms a viscous body, suggesting a greatly enlarged section of gelatin gel corresponding roughly to a net structure. When heat is applied the individual hide pieces a t first curl up gently and separate, and with rising temperature excrete gelatin. The pieces continue to contract and curl into tighter and tighter spirals or balls, depending on their original form and dimensions, until the mass becomes quite mobile, resembling melted gelatin with the solid particles as dispersed phase. This is not intended as a parallel t o gelatin behavior but as a picture of a mechanical transpiration. It is quite within the bounds of reason, and not incompatible with the principal mathematical theories of colloidal behavior, to assign to gelatin particles an elastic fibrilla structure in the gel state, the individual fibers swollen by imbibition until they cohere, forming as a whole an elastic gel or multiple effect of the individual fibrils. When heat is applied the fibers shrink, excreting the imbibed water of swelling. As the temperature is increased the threads begin to curl up and separate and with rising temperature contract into Firm gel
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INDUSTRIAL A S D ENGINEERING CHEMISTRY
Partial gel
This condition would present the appearance of a flocculent suspension. During partial hydrolysis it is conceivable that close spirals and threads or fibrils may exist simultaneously in the gelatin solution. Zsigmondy and Nageli concluded, from investigations with the ultra-microscope, that gelatin and semiliquid hydrosols show a granular or flocculent structure. Later investigations of Zsigmondy and Bachmann developed the suggestion that, in addition to the apparent grainy structure previously observed, there is also present a fibrilla or crystalline thread structure, This reference, as well as a summation of other theories of gel structure, is given by B ~ g u e . ~ ~ - ' S An interesting parallel to the conception of gelatin structure just described is furnished by Harrison.* Under favorable conditions he was able to prepare cholic acid crystals, among which, he states, "one often finds spiral-shaped crystals which twist first one way and then the other as the water molecules bombard them. The movement reminds one of spiral bacteria present in teeth.'' Nearly all highly flexible or elastic substances tend to curvature under the influence of heat. This is due sometimes to unequal tension of surface skin as a result of dehydration or oxidation, sometimes to the effect of strain, expansion or contraction, or other shifting of the normal structure. Viscosity and Jelly Strength
The simplest conception of the mechanism of jelly formation and viscosity is to assume that jelly strength depends upon the relative volume and number of individual fibrils present in the gel condition, while viscosity depends both upon their thickness and length in the sol condition. The thinner, shorter threads will contract into smaller spirals or spherites, resulting in greater mobility with correspondingly lower viscosity. After this manner of reasoning, viscosity may be considered a function of the average cross-section area of the threads in the form taken by them in the sol condition, and for equal average thickness the viscosity will vary with their number per unit volume. Permanent loss of viscosity of gelatin-water solutions, either in whole or in part, is known to be a resultant of time and temperature. When the time and temperature are sufficient the elastic limit of some of the spherites, either from excess local heating or inherent weakness, wiI1 have been exceeded and they will no longer be capable of resuming their original thread form on cooling. The spherites so affected will cease to contribute in full measure to the viscosity of the solution. As a consequence a depression of
Partial sol
Figure l - C o n c e p G
tighter and tighter spirals, finally approximating spherites, but not quite. If the temperature has not been toohighor too long continued, the fibrils retain their elasticity and ability to resume their original form on cooling, a reversible phase characteristic of gelatin-water mixtures. Hydrolysis and loss of setting power of a gelatin gel is a consequence of time and temperature. When the temperature and time are sufficient the spherical form of the fragments may become fixed, the elastic limit of the threads exceeded, and permanent deformation result (Figure 1).
Sol
Hydro-sol
of Gel-Sol Transit
viscosity will be noted, the more, the higher the temperature and longer the time. The transition of gelatin-water mixtures from the gel to the sol condition is continuous. Nevertheless, there must be some restricted range of temperature and concent,ration wherein the true forces governing viscosity are best revealed. Loebg considered that in gelatin solutions two opposite processes-the formation and dissolution of solid aggregates-go on simultaneously. I n other words, gelatin is always either setting or melting. At low temperatures the
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formation exceeds the dissolution of solid aggregates; this is the setting phase. At high temperatures dissolution exceeds formation, which is the melting phase. Obviously a t some temperature there exists an equilibrium phase. For a 2 per cent solution at p H = 2 Loeb finds equilibrium a t about 35" C . Bogue'O gives it a t 35-37' C. for gelatin a t pH = 4.7. Davis and Sheppard find equilibrium at 38" C. Such data suggest that viscosity measurements be made within that range of temperature a t which a gelatin solution is neither melting nor setting, which, for solutions of low concentrations at least, is at about temperature 37" C. The writers' o b s e r v a tions, made from a P l a r g e n u m b e r of m e a s u r e m e n t s of $t21 different types and 0 grades of gelatin un:: der widely divergent 5 conditions, indicate that the equilibrium range varies some1 1 I I I I I I I what with the conI I
)
'
Vol. 19, No. 2
results of this work are shown on the accompanying charts. For the measurements a capillary tube viscometer (Edible Gelatine Research Society) was used. The pipet was No. 84 and delivered 100 cc. of pure water at 20' C. in approximately 17 seconds. The procedure with each experiment was initially the same. The gelatin was heated in a constant-temperature water bath to 58" C., then quickly cooled to the temperature desired for making the test. A group of 3 per cent solutions of gelatin was prepared, cooled to, and held at 24' C. Viscosity was determined a t 10-minute intervals. The result was similar to that found by Loeb, the curve of increasing viscosity being practically the same as his. (Figure 2, curve a). Two other groups of the same gelatin were prepared, but immediately before taking each 10-minute test, the solution was warmed in one case to 32" C. and in the other to 40" C. These are a little each side of the theoretical transition o r true solution temperature. No change in viscosity with time was found for either group (Figure 2, curves c and d). The increase found in the first experiment was therefore not permanent. Nothing new is claimed for this observation, but should be remembered for that which follows. A fourth group was then prepared, using the same gelatin and procedure as before. The tests were made a t two temperatures. At each time interval the viscosity was taken
50
-
2% 5
-
T~me ili M i ~ u r i i
Figure 3-Retardation Effect o n Viscosity Increase o n Standing with Moderate Agitation
below 35' C. and to decrease a t higher temperatures. Granting this for the present, there is in consequence a limited range of temperature wherein no viscosity change occurs in a reasonable time. For want of a better designation we shall call this the true solution temperature. Experimental Procedure
The writers decided to investigate the sensitiveness and degree of this viscosity change and a t the same time to determine, if possible, why the change takes place. The
, , > ;2 % =i e t P 6 ? ,
I
I
"d -t 2 6 .
1
V$> d e b '
111
February, 1927
INDUSTRIAL AND ENGINEERING CHEMISTRY
The entire cycle of gel-sol transition is probably not uniformly continuous, but exhibits rather sharp changes, notably in three principal phases-the swelling, melting, and permanent deformation (loss of setting power) of the gelatin particles. The fact that we may, within reason, swell and shrink the gelatin particles a t w i l l and still preserve the original viscosity et true solution temperature seems to indicate that the number of gelatin particles present in any unit volume remains constant through all phases, the difference being in the magnitude of imbibition. This last factor, as already suggested, depends upon the relative volume or concentration of gelatin in water. Concentration equilibrium is that m 55
Fr4 Y5
I'
t w
7-79
l
35
j__.I.
5 25 ,
71,
2r 1 1,
Figure %Effect of Standing a t High and Low Temperatures for 5 Per Cent Low-Viscosity Gelatin
state in which the quantity of water is just equal to the capacity of the gelatin to absorb it. This condition should be fulfilled for a study of specific viscosity. It will be sufficient to note that gelatin solutions exhibit three phases-the jelly or setting phase, the equilibrium or true solution phase, and the melting phase. I n the setting phase, viscosity will increase with time, as Loeb found. This, as previously noted, is really a measure of increasing or incipient jelly strength, and not of real viscosity. I n the equilibrium or true solution phase, no viscosity change takes place in reasonable time. This must be true if viscosity &s a physical property is to be regarded as having a fixed value for any specimen of gelatin. I n the melting phase, gelatin solutions, especially those of low concentration and at high temperatures, show a progressive diminution of viscosity which is not restored on again cooling. This loss is permanent and the apparent gain of viscosity with time, measured a t low temperatures, is likewise not permanent, the normal viscosity persisting when the gelatin is reheated to within the limits of true solution temperature.
255
being 30 seconds (Figure 3, curve A ) . Curve b, Figure 2, for which an individual solution was used a t each interval, shows a gain of 29 seconds in only 23 minutes-a time ratio of about 5:l. Beginning with the seventeenth reading (170 minutes) the increase in apparent viscosity is more rapid, tracing a smooth curve. The limit is reached after 290 minutes, when the solution became too viscous to run through the capillary. The gel was then remelted to 32" C. and quickly cooled to 26" C. The original viscosity was restored. Undisturbed and under the same conditions t,his specimen will form a gel in little more than one hour. The frequent disturbance of the solution during the testing intervals retarded the jelly formation to nearly 5 hours. Moderate agitation therefore delays jelly formation, but does not appreciably affect viscosity. For direct comparison curves a and b from Figure 2 are plotted on Figure 3 to the same scale. Persistence of Setting Phase
After a gelatin solution has remained in the setting phase for several hours it requires considerable time to regain its normal viscosity at a higher temperature (Figure 4,A and B ) . The solutions were prepared in the usual manner and the viscosity of each was taken a t 26 O C. The group represented by curve A , however, was cooled to 24.5' C. and held at that temperature, but just before taking the viscosity reading a t each interval the solution was warmed quickly to 26" C. The solution represented by curve B was cooled to 26' C. and held so throughout the experiment. Since the viscosities of both groups were measured a t the same temperature, the difference in the curves represents the persistence of the setting phase or relaxation period. Reducing the concentration of a gelatin solution lowers the setting temperature and increases the time required to form a jelly. Curve C, Figure 4, represents a 2 per cent instead of a 3 per cent solution of the specimen used for curves A and B. The procedure was the same as for B. The apparent viscosity increase is comparatively small, only 21 seconds in about 4 hours, whereas the 3 per cent solution increased 144 seconds in the same time. I
I
Effect of Agitation
It has often been stated in the literature that agitation or frequent passing of gelatin through a capillary tube depresses the viscosity. The writers have found that gelatin will not set a t all if held within the region of its true solution temperature or above. This may be comparatively low for some specimens (Figure 5, Nos. 7679 and 7806). At lower temperatures the gel is formed more rapidly when held undisturbed. Agitation retards the setting point considerably. I n order to show this effect the specimen used in the previous experiments v a s chosen. Only one solution was prepared in the usual manner, and cooled at once. This solution was run through the viscometer at 10-minute intervals, the temperature remaining a t 26 " C. throughout the experiment. For the first sixteen measurements (160 minutes) the apparent viscosity increase proceeded a t a uniform rate of about 2 seconds flow for each 10-minute interval, the total increase
Figure 6-Showing
Restricted Range of Viscosity Values at 6
Per Cent Concentration and 60' C.
Curve D, Figure 4, represents a 2 per cent solution of a weak gelatin. The treatment was the same as for curve C. I n this case there is no change of viscosity with time. Evidently we are well above the jelly point of this sample, or at least the process of setting is extremely slow even at this low temperature.
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INDUSTRIAL AND ENGIiVEERING CHEMISTRY Tests on 5 Per Cent, Low-Viscosity Gelatin
Weak gelatins show no change of viscosity with time a t relatively high concentrations. Two samples were chosen, both having a jelly strength of 130 grams Bloom (Figure 5). Sample No. 7679 was at pH = 5.65; KO.7806 at pH = 4.40. The concentrations were 5 per cent. Each group consisted of seven individual solutions, one for each test. Viscosity was determined a t 10-minute intervals. Each sample was meas-
Vol. 19, No. 2
ments made in these experiments show that at 60" C. the fluidity of gelatin solutions is too great to indicate their actual difference in viscosity. Figure 6 shows curves of gelatins Nos. 7573 and 7539, of different concentrations. It will be seen that at 6 per cent concentration the total range between gelatins of high and low viscosity is 26 millipoises. In other words, the entire range of viscosity measurements for average gelatin of commerce must fall within this small scale, so that two
--,
Viscosirr m p
Effective Range of Temperature for Viscosity Measurements
Figure 7-Showing Advantage of Measuring Viscosity a t 10 Per Cent instead of 6 Per Cent Concentration
Figure 8-Showing
ured a t two temperatures, 26" and 60" C. The results show no viscosity change for either sample, a t either temperature. These experiments tend to prove that change of viscosity with time, according to the definitions quoted, is an accidental feature, depending on the choice of the specimen, the concentration, and the conditions. Moreover, the change is only in apparent, not real viscosity. Once real viscosity has suffered change, the change is irreparablethe gelatin structure is physically deformed, the elasticity permanently injured. If care be taken to differentiate properly between real and apparent viscosity, and if the factors involved are made clear, the effects due to time, temperature, and concentration will be assigned a proper value. As i t is, much confusion and disagreement prevail.
specimens having small differences are hardly distinguishable from each other. At the same temperature using a concentration of 10 per cent the range is 68 millipoises, which permits of considerably greater latitude and serves as a better indication of viscosity differences. This effect is strikingly shown in Figure 7. Two pairs of curves of the same gelatin samples are shown, one measured at a concentration of 6.66 per cent, and the other a t 9.3 per cent. It will be noted that the 6.66 per cent concentration viscosity of the two samples is the same a t 60" C. At 55" C. a small difference is shown and a t 50" C. a still greater difference occurs. From this point to 40" C. the difference appears constant but still too small for practical use. At the 9.3 per cent concentration the two curves are practically parallel from 60" to 45" C. Obviously, then, either lower temperature or higher concentration than that recom-
Practical Viscometry
The viscosity measurements shown in Figures 6 to 10, inclusive, were made to find the most suitable concentration and temperature for viscosity determinations of average gelatin. The wide viscosity range of average commercial gelatin necessitates some compromise, but for special work a study of the first part of this paper will indicate a suitable procedure. Two typical specimens were chosen, designated as Nos. 7573 and 7639, the former being representative of average low-viscosity gelatin and the latter of average high-viscosity gelatin. In addition, Kos. 7334 and 7573, both in the lowviscosity group, were measured a t two concentrations and over a range of temperatures from 40" to 60' C., in order to indicate the temperature and concentration at which the difference between the two specimens is most clearly shown. A series of measurements was also made of gelatins a t different concentrations, in order to determine what condition will give the widest practical range for both high- and lowgrade gelatins. It has been observed in this laboratory that when two gelatins are nearly alike in viscosity, the difference is not shown when viscosities are measured according to the Edible Gelatine Research Society standard, which specifies a concentration of 6.66 per cent and a temperature of 60" C. The measure-
Figure 9-Showing
Constant Difference or Straight-Line Period
mended by the Edible Gelatine Research Society is required to indicate true relative viscosities of gelatin in this group. Figure 10 shows the same effect in another way. When any group of gelatin solutions is a t temperature equilibrium, the viscosities a t higher concentrations, within limits, are
February, 1927
I S D U S T R I A L A S D EATGIXEERING CHEMISTRY
parallel functions. With the weaker gelatin (lower curves, Figure 10) the difference in viscosity of the pair increases with the concentration. Ehidently, the true solution or equilibrium temperature for this group is well below 40” C. The initial viscosities of this pair are practically alike. -It is evident that a concentration of 6.66 per cent at a temperature of 60” C. is not practical for this class of work. From Figure 8 it will be noted that a t a Concentration of 6.66 per cent the differences for type 9gelatin are constant between 40” and 55” C. and for type B gelatin between 50” and 60” C. Accordingly, t h e best a v e r a g e temperature for this concentration lies somewhere between 45 ” and 50’ C. but since the deflection from the straight line at 45” C. in B is not very great and since this temperature falls well within F i g u r e ¶&-Showing Parallel F u n c t i o n the straight-line Portion for C o n c e n t r a t i o n s above 10 Per C e n t of type A gelatin, if a within L i m i t s concentration of 6.66 per cent is to be used the temperature should not exceed 45O Figure 9 shows curves of two specimens, No. 7573, an average high-grade, and KO. 7639, an average low-grade
c.
257
gelatin. Here again the straight line OY,constant difference part of the curve falls between 45” and 55” C. It seems clear that any temperature falling within this straight-line period would be satisfactory for gelatin testing, but in order to show distinctly small viscosity differences, it would be better to choose a concentration of 10 per cent a t temperature 40’ to 45” C., as these conditions provide the widest practical range and have proved to be the most easily duplicated by different observers. This temperature is also one that can be kept more nearly constant under ordinary working conditions, and low-grade gelatins especially are not liable to degrade so quickly at this temperature as at higher temperatures. Furthermore, no special precautions are necessary. The viscosity change under these conditions will not be appreciable for several hours. The containers should, of course, be covered during the holding period in order to avoid loss of water from evaporation. Bibliography 1-Loeb, “Theory of Colloidal Behavior,” p. 282, McGraw-Hill Book Co., 1924. a-Proctor, Rept. Faraday SOC.and Phys. SOC. London, p. 34 (1920). a-Barrett, I b i d . , p. 49. 4-Loeh, o p . c i L , p. 273. &-Briefer. Trans. SOC.Molion Picture Eng., No. 18. 185 (1924). 6-Bogue, “Applied Colloidal Chemistry,” Vol. I, p. 240, McGraw-Hill Book Co., 1924. 09. c i l . , p. 40 ?-Proctor, 8-Harrison, Ibid., p. 58. g-Loeb, op. c i t . , p. 283 10-Bogue, “Chemistry and Technology of Gelatin and Glue,” p. 151, hlcGraw-Hill Rook Co., 1922. 11-Bogue, “Colloidal Behavior,” Vol. I, p. 377 (1924). and Phys. Sor. London, p. 52 (1920). 12-2sigmondy, Rept. Faraday SOC. la-Reiger, Physik., 13, 241 (1913). 14-Fraas, Hatschek, Rept. Faraday SOC.and Phys. SOC. London, p. 31 (1920). l+Bogue, “Colloidal Behavior,” Vol. I, p. 390 (1924).
What Is Chemical Engineering ?’ By Harry A. Curtis STERLING CHEMICAL LABORATORY, YALE UNIVERSITY, NEW HAYEN,CONN.
Early History
HAT is chemical engineering? Chemical engineering is an art which tvas practiced and fairly well developed long before the science of chemistry was spawned. Robert Boyle is usually accused of being the father of scientific chemistry. Some say it was Lavoisier, presumably having in mind the bad end to which the great French savant finally came. Boyle was a t the height of his career about 1660, Lavoisier more than a century later. What of the chemical engineers in 1660? The history of chemical engineering has not yet been written, but it is well known that in 1660 the chemical engineers of the day were planning, constructing, and operating plants according to the best information available. They were extracting metals from their ores by a variety of processes, some of them strictly chemical; they were purifying the metals by subsequent chemical operations; they were manufacturing in quantity and by factory methods such materials as gunpowder, incendiary bombs, saltpeter, several of the common acids and their salts, a variety of paint pig1 Presented as a part of the Symposium on “Chemical Bngineering” before the Division of Chemical Education a t the 72nd Meeting of the American Chemical Society, Philadelphia, Pa., September 6 t o 11, 1926.
ments, soap, glass, perfumes, alcohol, sugar, and a large number of what we call today, chemical products. They were building and operating furnaces of many kinds, filters, stills, rectifying columns, driers, evaporators, grinders, and other pieces of what we today call chemical plant equipment. Let us grant that these fellows did not know much of the theory of evaporator design; about as much, let us say, as the average chemist does today. Nor were they able to write chemical reactions for the processes which they carried out. But they built chemical plant equipment and carried out chemical processes on a commercial scale just the same. They used what they could of the sciences then available; they drew on the fund of experience which was common in their profession; and when neither science nor experience was available they guessed, and guessed again, just as their successors must do today. But they produced the goods-that is the important point-and, as time went on, they produced them ever better and cheaper. Were they chemists? Well, not of the “pure” variety which traces its ancestry t o Boyle or Lavoisier. Were they engineers? Let us see what we mean by the term. “Engineer = one who carries through an enterprise by skilful or artful contrivance.” These men were certainly carrying
