Oct., 1 9 1 j
T H E J O 1 7 K S . l L O F I S D C S T R I A L A N D ELTTGINEERING C H E M I S T R Y
t h u s obtained for t h e accurate determination of t h e specific gravity' of t h e mixed iodides at I 5 . 6 C. I\'-From t h e specific gravity t h u s obtained calculate t h e percentage b y volume of methyl alcohol in t o t a l alcohol ( c y ) b y t h e following formula:
(%:) of mixed iodides GI = 2 . 2 9 2 ; specific gravity (15.6O C./15.6' C.) of methyl iodide and G2 = 1.947; specific gravity (15.6' C./15.6' C.) of ethyl iodide
where G = specific gravity
Subtracting t h e percentage of methyl alcohol t h u s obtained from I O O gives t h e percentage of ethyl alcohol ( p ) . F r o m these values, t h e percentage of total alcohol by lT-olume is readily calculated b y Formula I11 a n d t h e n t h e percentage b y volume of each in t h e varnish. If t h e percentage of methyl alcohol in t o t a l alcohol falls below I O per cent, t h e following procedure based on t h e Riche a n d B a r d y method for t h e detection of methyl alcohol will be found t o give quantitative results of greater accuracy t h a n is possible b y t h e specific gravity method. T w o s t a n d a r d solutions, one of absolute e t h y l alcohol a n d t h e other containing a mixture of I O per cent b y volume of absolute methyl alcohol a n d 9 0 per cent b y volume of absolute ethyl alcohol, are treated t o form t h e iodides a n d distilled a n d purified as described above, a n d t h e n subjected t o t h e following t r e a t m e n t together with t h e u n k n o w n : Place j cc. of t h e iodides with a n equal volume of aniline in a 2 0 0 cc. narrow neck flask, stopper t h e flask a n d allow t o s t a n d over night in a dish of water a t room temperature. I n t h e morning a d d r j o cc. of water, heat till t h e water just begins t o boil, a d d a b o u t 3 0 cc. of I O per cent caustic soda solution a n d t h e n water until t h e light oily layer of dimethyl a n d diethyl aniline is brought into t h e neck of t h e flask. Pipette I cc. of t h e oily layer into a small porcelain dish a n d mix it well with I O grams of a n intimate mixture of I O O p a r t s of clean sand, 3 p a r t s of finely powdered cupric n i t r a t e , 2 a n d 2 parts of finely powdered sodiu? chloride. Heat t h e dish in a n oven at 90' C. for a b o u t 8 hours, occasionally stirring t h e mixture a n d breaking u p t h e lumps t h a t may form. T h e n transfer t h e entire contents of t h e dish t o a I O O cc. graduated flask with h o t 9 j per cent alcohol, using not more t h a n 80 cc. of alcohol in all, a n d boil for a b o u t 20 minutes. Cool t h e flask, make u p t o t h e mark with 9 5 per cent alcohol, shake, allow t o settle, pipette I cc. of t h e solution into a 500 cc. graduated flask a n d fill u p t o t h e mark with water. B y mixing t h e s t a n d a r d solutions t h u s obtained f r o m t h e absolute ethyl alcohol a n d t h e mixture containing 90 per cent of ethyl alcohol a n d I O per cent I Where time permits, it would be well t o run blanks for specific gravity determinations, with absolute metliyl and ethyl alcohols, t o prevent differences that usually occur with different operators owing t o personal equation, etc. The cupric nitrate must be very finely powdered and the component parts must he intimately mixed in order t o make the colorimetric test sufficiently delicate for quantitative work and the mixture used for the standards must be identical with that used for the unknown determination, since different mixtures give different intensities of color with the same quantity of dimethyl aniline.
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of methyl alcohol i n t h e proper proportions, make u p standards ranging from I per cent methyl alcohol t o 9 per cent methyl alcohol, leaving enough of t h e initial standards t o use for comparison also. Nom compare t h e unknown solution with these standards either in Nessler tubes or a suitable colorimeter. I n case t h e unknown has a t i n t between a n y t w o of t h e standards, b y further dilution of these, t h e percentage can be determined t o t e n t h s of a per cent. If t h e shade of t h e unknown is deeper t h a n t h e I O per cent s t a n d a r d , i t may be matched with t h e standard b y dilution, b u t t h e variation from t h e standard must not be great or t h e method becomes inaccurate. U S CUSTOMS LABORATORY P O R TOF hTEwYORK
NEPHELOMETRY' (PHOTOMETRIC ANALYSIS) I-HISTORY OF METHOD AND DEVELOPMENT OF INSTRUMENTS B y PHILIP ADOLPH KOBERA N D SAR.4 STOWELL GR.4VES Received June 14. 1915
INTRODUCTION
Quantitative analysis i n t h e past has depended chiefly upon t h e production of precipitates, more or less insoluble. Cntil recently these precipitates have been separated from their surrounding media either through filtration or sedimentation, a n d in most cases washed, dried a n d weighed. T h e object of these manipulations, which require considerable practice a n d skill, is, of course, t o determine t h e mass or weight of t h e precipitate itself. 411 chemists know how much time, skill a n d patience i t takes t o accomplish t h e separation, purification a n d meighing of precipitates. I n applied chemistry, where colloids a n d similar interfering substances are met, t h e lot of a chemist who endeavors t o estimate substances gravimetrically is not a h a p p y one. Fortunately, t h e analyst is not entirely dependent on gravimetric analysis, b u t for m a n y substances, volumetric a n d colorimetric methods ha\-e been developed. which often are equally as accurate a n d save cons i d e r a b 1e time. Nevertheless, the great number of estimations depend, as is known. on gravimetric methods. For this reason a photometric method of analysis, called nephelometry, has been developed, which a t t e m p t s t o FIG. FIRST STEP IN T H E DEVELOPMENT estimate t h e mass or OF NEPHELOMETRY The amount of precipitate was gauged
weight Of precipitate roughly with the eye. (1859 Mulder.) i n a solution directly, i. e . , without filtering, washing a n d weighing. T h e n a m e is derived from t h e Greek word "nephel," meaning a cloud. 1 Read before the New York Section of American Chemical Society, Chemists' Club, June 1 1 , 1915.
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T h e basis of t h e method is t h e measurement of t h e brightness of t h e light reflected by a cloud-in other words, by t h e particles in suspension-very much as in a n ultramicroscope. T h e intensity of light reflected is a function of t h e quantity of suspended particles, when other conditions are constant.
Vol. 7 , No. Ia.
by Professor Richards of H a r v a r d , in 1894,in connection with his atomic weight work on strontium. T w o test tubes were slightly inclined so t h a t one could n
A
H I S T O R Y OF M E T H O D
The principle of t h e method may be seen most easily by-tracing its development. Fig. I shows how,
A
Sia.
TRII
FIG.3 FIG.3-FIRST
FIG.4
KEPHELOMETER. Made by Richards in 1894. Substance. contained in two test-tubes; observed from above Sliding jackets (graduated) were used to match the light reflected. FIG.+SECOND NEPHELONETER. Made by Richards and Wells in 1904. The sensitiveness of the instrument was increased by painting the ends of the tubes and inserting two prisms.
loolfinto both with one eye, without moving. Around the test tubes were two opaque sliding jackets. When t h e slides were adjusted so as t o give equal opalescence in t h e two tubes, t h e precipitates were assumed t o be
I
FIG.2 4 E C O N D STEP I N THE DEVELOPMENT OF NEPHELOMETRY The amount of absorbed light was compared to t h a t of a standard. Used by Stas in 1874. Light was reflected from illuminated scale through tubes, containing precipitate, to the eye.
when two test tubes were held side by side a n d t h e amounts of turbidity were roughly compared, t h e first step in t h e development of nephelometry was taken. T h u s , Mulder, in 1859, roughly compared opalescent silver chloride suspensions obtained in his filtrates from atomic weight determinations. Fig. z shows t h e use, b y Stas in 1874,of a series of tubes, a b o u t 4 cm. in diameter, with perfectly plain bottoms. Four tubes were supported adjacent t o each other upon a shelf over holes of nearly t h e same diameter. Beneath t h e shelf was placed a n illuminated scale a n d everything above t h e shelf was kept in darkness. When t h e marks on t h e scale viewed through t w o heights of opalescent solution appeared equally illuminated, Stas assumed t h a t there was a n equal weight of precipitate in t h e t w o tubes. I t will be observed t h a t Stas measured t h e absorbed light, which for fine, white clouds is not nearly a s sensitive a s t h e reflected light. This will be shown a n d discussed in detail later. Fig. 3 shows t h e first real nephelometer, made
FIG. 5-THIRD KEPHELOMETER Made by Kober in 1912, from a Duboscq colorimeter with wooden attachments. This instrument eliminated errors due t o the meniscus and produced a much better optical equipment.
present in amounts inversely proportional t o t h e length exposed t o t h e light. Ten years later, in 1904, Richards a n d Wells
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T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
made a number of improvements in t h e apparatus, a n d Fig. 4 shows t h e improved instrument. T h e tubes destined t o hold t h e solutions under examination were test tubes free from striations, holding about 3 2 cc. a n d painted black around t h e t o p a n d bottom with asphaltum paint. These opaque bands formed t h e most convenient method, according t o t h e authors, of obliterating reflections from t h e meniscus a n d from t h e curved bottom of t h e test t u b e . The n e p h e l o m e t e r designed by Richards, in order t o obtain a correction for his atomic weight work, was used t o estimate small a u a n -
845
This instrument gives very good results, b u t has a number of disadvantages: ( I ) Only about 40 mm. height of liquid can be used. ( 2 ) Repeated painting of t h e plunger is necessary because of t h e solvent action of some liquids, a n d t h e chipping off of paint through use. (3) The cost, as it now stands, paying d u t y on t h e Duboscq colorimeter, is close t o $100.00.
FIG.6-FOURTH h7EPHELOMETER Similar to the third b u t with metallic attachments substituted in the place of the wooden. Made by Kober in 1913.
tities Of substances which he found in his filtrates. Richards expressly stated t h a t t h e instrument was not intended for determining large amounts of substances. Since t h e nephelometer described b y Richards a n d Wells yields its best results only on taking a large number of readings, a n d since for practical work so much time for readings is objectionable, a n improvement was highly desirable. I t was thought t h a t a similar instrument of greater accuracy which would yield reliable results n-ith a few readings, comparable t o those obtained Kith a Duboscq colorimeter, would greatly enhance t h e value of t h e nephelometer for t h e chemical analyst. S o doubt the Richards instrument sufficed for the purpose for which i t was designed, a n d therefore efforts t o impr0T-e t h e instrument were heretofore superfluous. However, since a n instrument was desired, not simply t o yield a slight correction t o some other analytic process itself, b u t t o yield all t h e figures of t h e determination, greater accuracy was now require d. D E V E L 0 P h1 E N T 0 F I N S T R U M E N T S
Without going into t h e various considerations connected with t h e construction of t h e nephelometer, developed in t h e Harriman laboratory, it is sufficient t o say t h a t t h e optical workmanship of t h e Duboscq colorimeter proved t o be a n excellent basis o n which t o build a nephelometer a n d Fig. 5 shows our first nephelometer. I t was made b y one of us, without any special tools, from small packing box boards. T h e parts, however, owing t o moisture, soon warped a n d metal parts had t o be substituted as may be seen in Fig. 6. T h e only changes necessary were a coat of black asphaltum paint on t h e plungers, a special nephelometric t u b e a n d a metallic receptacle for t h e same. T h e great advantage besides increased accuracy, in this instrument, is t h a t i t is still usable as a colorimeter, as t h e change from colorimeter t o nephelometer a n d vice versa can be made in a few minutes.
B
FIG. 7-oPTICAL EQUIPMENT OF THE h'EW INSTRUMEWT Designed by Kober and shown for the first time. B-New plungers which change the height of liquid under observation. C-New arrangeof ment of prisms, which gives a Lummer-Brodhun effect. D-Lenses terrestrial eye-piece. E-Appearance of field; right-hand plunger changes light in the square, left-hand plunger changes light in circular space.
As it was impossible t o get these French instruments a t any price, owing t o t h e war, we have had built, through t h e firm of Lenz & Naumann,' a new instrument, along t h e lines of a Duboscq colorimeter, b u t embodying all t h e latest results of our own experience. Fig. 7 shows a n almost ideal plunger, obtained after much experimentation. T h e end of t h e plunger of optically perfect glass was fused or melted t o t h e black glass sides, t h u s making it impervious t o all kinds of solvents, a n d eliminating cement troubles once for all. Fig. 7 also shows t h e optical arrangements, a n d t h e construction of t h e prism a n d eyepiece. This gives a Lummer-Brodhun field, which 1
Pullman Building, 17 Madison Ave., New York City.
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T H E J O U R N A L O F I N D U S T R I A L A S D ELVGIXEERIiVG C H E M I S T R Y
increases t h e sensitiveness of t h e readings. Fig. 8 shows t h e latest form of t h e instrument a n d also t h e operation of a dark curtain which cuts down stray reflections a n d always insures a black background. Furtherm o r e , t h e instrument can be inclined a t a n angle a n d securely fastened there. The holes in t h e base permit one t o screw the instrument tight t o a table or other s u p p o r t s and thus prevent t h e apparatus from being jarred or FIG.8-XEW INSTRCMEKT accidental1 y Designed by Kober, made b y Lenz & Naumann. moved out of New York. -4s may be observed black curtains t h e correct range operate with the cups, always insuring a black background of t h e light. The graduations for reading t h e heights of liquids are so constructed t h a t t h e y are adjustable a n d can be set exactly on zero, when there is zero light or color in t h e instrument. 44t least I O O mm. of liquid may be used, t h u s enabling us t o estimate finer clouds a n d smaller amounts of substances. This instrument, “ m a d e in America,” in fact in this city, can be obtained for $36.00, t h u s reducing t h e cost some 300 per cent besides giving all t h e improvements just mentioned LIGHT-Accuracy in nephelometry is dependent on t h e uniformity a n d constancy of t h e light thrown upon t h e tubes. illthough errors due t o uneven distribution of light may in most cases be eliminated b y careful standardization of t h e light, the errors due t o changes or inconsistency in distribution are beyond control. Attempts t o develop a n ideal nephelometric light, i. e., one in which t h e rays are both parallel a n d uniform, have t h u s far not been very successful, b u t t h e lamps shown here (Fig. 9) are t h e best t h a t we have been able t o obtain, after two years of experimentation. The object in trying t o get parallel rays is t o eliminate a s much as possible t h e zero light of t h e i’nstrument. The theoretical qualifications for such a light are: ( I ) a point source of light, t h a t can be conveniently attached t o ordinary lighting circuits; ( 2 ) a n optical system, t h e simplest being t h e Ramsden ocular, for making t h e rays parallel (Fig. I O ) . Arc lights being excluded, t h e simplest form would be a filament lamp, where t h e filament was very compact. The compactness of t h e filament .obviously depends on t h e length a n d thickness of t h e filament, b u t as most filaments are very fine, t h e main difficulty was encountered in t h e length. If low voltage had been available, say six volts ( t h a t of 2 t o 3 storage
Vol. 7, NO. I O
cells) , correspondingly shorter filaments could have been used, making t h e task much easier. Although storage cells are in universal use, for pleasure and business in automobiles, yet t h e introduction of t h e m for nephelometric lights would almost make the price prohibitive. I n these new lights parallel rays are practically obtained, b u t for many purposes a n ordinary powerful filament lamp well screened held about three feet from t h e instrument will give good results. These lights, a s well as other attachments, can be obtained from t h e firm of Lenz & Naumann. GENERAL CONSIDERATION
As t o t h e accuracy obtainable with this t y p e of nephelometer, t h e following figures will suffice: Two solutions of casein were made, unknown t o t h e analyst. One was t o serve as a standard, t h e other as a n “ u n known.” The following readings were obtained: READINGS I N MM. S T A N D A R D1 4 . 0 13.8 14.1 14.1 UNKNOWN 14.9 15.1 15.1 15.1 Ratio of Unknown t o Standard.. . . . . . .
. ..
Averag 14.03 15.06 . . . . . . . . . . . . . . . . . 0,921 14.1 15.1
14.1 15.1
T h e standard was made b y taking 2 j cc. of stock solution, a n d t h e “ u n k n o w n ” by taking 2 3
FIG. 9 a - I i ~ w I N S T R U M E N WITH T LAXP HOUSE A-Screw for changing slope of instrument t o suit the convenience of observer. L-Light. 0-Ocular, which produces almost parallel rays of light. C-A mirror (removable) inserted when the instrument is used as a colorimeter, which throws the light on M , the regular colorimeter mirror for holding liquid. either colored or containing a or reflector. T-Cups suspension. P-Plungers. H-Prism house. E-Terrestrial eye-piece. RRack and pinion which moves cups up or down. When mirror ( C ) is not used light falls on tube (T) a t right angles; ready for nephelometric work. When used for colorimetry, cups (T)which have clear, transparent bottoms, are used. When used for nephelometry, cups (suggested by M . S. Fine), of the same shape but having perfectly black, opaque bottoms, are used.
cc. a n d diluting t o 2j0 cc. T h e ratio, therefore, is 2 3 + 2 5 , or 0 . 9 2 0 , which makes t h e error in this case about 0 . I per cent. As has been stated, t h e nephelometer can be used only when t h e substance t o be determined is in t h e form of a suspension, which is stable long enough t o allow readings in t h e nephelometer before floccula-
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T H E JOURiVAL OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
tion occurs. d t the first thought one would expect t h a t t h e instrument is applicable t o only one class of substances. namely, colloids, b u t this is far from t h e t r u t h . Professor Harry Jones, in his book “ N e w E r a of Chemistry,” published before t h e development of nephelometric methods, states t h a t “precipitation.” meaning settling out of the s u b s t a n c e , ‘(is not the natural c o n d i tion in chemistry ” and, he adds, “is one of the most import a n t phenomena in all chemistry a n d m-e are so familiar with precipitation FIG.9 / ~ - l < X T E R I O W O F S l i \ v I S S T R U b l E S T A K D LaMP IICITiEE from our analytShow-., the scales v i t h vensiers: also doors which ical days t h a t n h e n closed pc.rmiL n o light to be seen except in we are accusthe eye-piece tomecl t o look upon i t as t h c natural condition when a. solid is formed as t h e result of a reaction between tn-o solutions. We see from t h e above (meaning some previous discussion) t h a t such is not at all t h e case. A moment’s thought will show v h y this is true. When substances react t h e y react. we believe: molecule for molecule. The solid when first formed either has molecular dimensions or there are only a few molecules of t h e solid aggregated.” He t h e n concludes t h a t “ t h e colloidal solution or at most t h e colloidal suspension is t h e natural condition of solid matter \\-hen first formed as t h e result of a reaction.” Our experience has shown t h a t t h e chief requisite for making these suspensions a n d for keeping t h e m as such for a definite time, is t h a t t h e substance b’e in a dilute solution, usually not stronger t h a n IOO milligrams per liter. Therefore t o apply t h e method t o large amounts of substance i t is only necessary t o dilute suitably. Clouds, produced by one p a r t in 500,000 of liquid, can also be determined quantitatively. Since, therefore. t h e amount of substance seems immaterial, it is important t o know whethcr t h e nature of t h e precipitate imposes any limitations on t h e method. I t is necessary t o consider: I. COLOR--If t h e precipitate is highly colored a n d remains in suspension, i t is best determined colorimetrically; if slightly colored, it is best determined nephelometricalll-. 11. F O R M O F PRECIPITATE-It must be colloidal, in the form of a suspension. A large number of precipitates found in practical work are colloids; a number are partly so, while some are so entirely crystalloidal, such as barium sulfate, t h a t they settle immediately. I n work published by us certain solutions of protective colloids have been used; such as egg
847
albumin a n d soluble starch, which causes crystalloids like barium sulfate a n d other partly colloidal precipit a t e s t o remain in suspension long enough for t h e application of this method. T h e n e p h e l o m e t r i c m e t h o d m u s t be u s e d f o r colorless colloidal s u s p e n s i o n s a n d f o r t h e a c c u r a t e d e t e r m i n a t i o n of a m o u n t s of m a t e r i a l w h i c h give no delicate color r e a c t i o n a n d a r e too m i n u t e t o filter, b u t w h i c h a r e d a i l y d e m a n d i n g o u r interest a n d a t t e n t i o n . T h e use of t h e method has been extended t o all classes of substances a n d since by careful work con-
FIG. IO-RAZISDEN
OCULAR
T w o plano-convex lenses, the convex sides facing each other.
(I,) Posi-
tion of point source of light.
siderable accuracy- can be obtained, t h e application promises t o be general in t h e different branches of chemistry. .-it a later meeting we hope t o have t h e privilege of discussing our theory and of describing t h e applications of nephelometry, t o t h e estimation of proteins, fats. uric acid a n d other purines, ammonia, phosphorus, silver, chlorides, acetone, a n d nucleic acids. HARRIMAN RESEARCH LABORATORY ROOSEVELT HOSPITAL, SEWTORECITY
THE EFFECT OF AMMONIUM CHLORIDE UPON FERRIC AND ALUMINUM HYDROXIDES DURING IGNITION By H. \T. DACDT Received M a y 1 7 , 1915
Complete removal of ammonium chloride from precipitates of ferric a n d aluminum hydroxides is commonly prescribed on account of t h e danger of formation a n d volatilization of t h e metallic chlorides. : i statement by Hillebrand’ t o t h e effect t h a t complete removal of ammonium chloride from aluminum hydroxide before ignition is unnecessary led t o t h e carrying out of experiments which completely confirm this statement. Approximately 0 . z g. of pure iron wire was weighed out after thorough cleansing by scouring with clean, wet sea sand a n d drying. Each weighed portion was dissolved in hydrochloric acid, t h e solution was oxidized with nitric acid. a n d ferric hydroxide was precipitated by adding t h e solution t o a n excess of redistilled ammonia2 in a platinum dish. After coagulation a t boiling temperature, t h e precipitate was washed b y decantation with the number of j o cc. portions of hot water indicated in t h e following table. After being collected upon a filter paper, i t was ignited t o constant weight in a weighed platinum crucible, finally with a blast lamp. 1 “The Analysis of Silicate and Carbonate R o c k s , ” U. S . Geol. Survey, Bull. 422, Xote C, p. 99 (1910). Baxter and Hubbard have shown ferric hydroxide t o be essentially insoluble in an excess of ammonia, J . A m . Chem. SOC.,28 (1906). 1508
