T H E J O r R L I T A LO F I N D C S T R I A L ALTD EIVGILVEERISG C H E M I S T R Y
I022
A-The crust proper trimmed off t h e entire slice. B-A section about 1/2 in. thick, next t o t h e crust. C-A second section 1;s in. thick. D-The innermost portion, in form of a cube.
The moisture was determined on every portion with the result,s shown in Table I : TABLEI-PERCEXTAGES
bIOISTURE I N P O R T I O N S O F A SLICE OF BREAD B C D Section next Section Inner KO. Crust t o crust .next cube 1. . . . . . . . . . . . . 25.50 40.78 42.98 42.60 2 ............. 18.79 32.27 38.42 38.69 3.. . . . . . . . . . . . 22.31 3 i . 57 41.70 41.67 OF
-4
Yol. 8 No. 1 1
cated in Fig. I! moisture being determined on every portion. These results are shown in Table 11-: TABLEIV-PERCENTAGES
OF ~ I O I S T U IT RE PORTIONS OF .I I,OAF BREAD COMPARED WITH T H A T OF THE ENTIRE 1,OAF A B C D E F Section Section Inner Crust of Crumb of Total in Crust next crust next cube 1 4 loaf 1 ’ 5 loaf 111 loaf 26.84 39.72 43.10 43.08 29.18 41.44 77.17
OY
Bread
Loaves similar t o the preceding mere then used t o determine how t h e moisture varies in slices taken from different portions of t h e loaf (see Fig. 11). These loaves were sampled as follows: .%-The end crust, about M in. thick. B-A slice immediately adjoining A and about 11s in. thick. C-A slice I/z in. thick c u t about half-way toward t h e center. D--A slice ‘/s in. thick directly from t h e center of t h e loaf.
The moisture content of every slice (crumb and crust together) was determined with the results shown in Table 11: TABLEII---PERCEiiTAGES
O F b1OISTURE IK DIFFERENT P A R T S OF COMMERCL4L BREAD5 .‘I B C D Bread Slice next Slice half-way Slice from ,TO. Crust to crust t o center center 1 . . . . . . . . . . . . 22.63 35.12 35.41 36.01 2. . . . . . . . . . . Z i . i 7 35.74 36.26 36.23 3. . . . . . . . . . l i , l l 30,GR 37.38 3i.i;
Having shown in this experiment t h a t t h e water content varies depending upon the section of t h e loaf from which a slice is c u t , the next step was t o determine t h e moisture of the loaf as a whole compared with t h a t of these slices Loaves of bread similar t o
FSG.
r
FIG.
I1
the preceding were used. These were cut in half and t h e moisture determined on slices cut from one half in a manner similar t o t h a t indicated in Fig. 11. The other half, E, was used entire, crust and crumb together, for a total moisture determination. These results are shown in Table 111: TABLE111-PERCENTAGIX
O F hfO1STURE I N DIFFERENTPARTS OF .4 L O A F BREAn COMPARED WITH TH.4T OF THE ENTIRELOAF A B C D E Bread Slice next Slice half- Slice from Half loaf No Crust to crust mav t o center center or total 37.70 37.45 35.14 1 . . . . . . . . . . . . 26.85 36.59 35.93 33.09 32.75 35.65 2 . . . . . . . . . . . 20.03 38.18 38.00 34.99 3.. . . . . . . . . . . 23.50 .35.32
OF
DISCUSSIOK OF RESULTS
I t is very el-ident t h a t t h e moisture content of t h e crumb varies considerably, depending upon its proximity t o the crust or t o t h e center of t h e loaf. I t might be supposed t h a t there would be a more or less regular increase in moisture as the sample approaches the actual center, b u t this does not seem t o be the case. I n fact, the results indicate t h a t there is no appreciable difference in moisture content in slices of bread taken a reasonable distance from t h c end of the loaf or in the crumb of any individual slice taken a reasonable distance from the crust. Therefore, after one gets fairly within the !oaf, it seems t o matter little whether t h e crumb be taken directly from t h e center of the loaf or not, since t h e variation is not great until rather near the end 01crust of t h e ].oaf. There is a great difference, hoxever, between t h e moisture in the whole bread (as det,ermined on one-half or one-yuarter of a loaf),‘ and t h a t in either the crust or crumb taken separately or in one entire slice. This shows t h a t in reporting the moisture content of bread it is necessary to stntc what portion of t h e bread was used. as well as how the moisture was determined. Another point that seems t o deserve attcntion is the age of t h e loaf. It is known t o every one t h a t bread loses moisture from the moment it leaves the oren. Consequently some idea of t h e freshness of the loaf should be given. When bread is baked in the laboratory it is usually weighed from I t o 2 hrs. after leaving the oven. When loaves are bought on t h e open market it is not always possible t o know honlong t h e time since baking, b u t this will almost always be less than 24 hrs. I n conclusion, t o determine t h e moisture i n bread use one-half or one-quarter of a loaf, depending upon the character of t h e crust, and follow t h e method described on page 1 0 2 1 . This is a far more simple as well as more accurate method t h a n t o find t h e proportion of crust t o crumb and t o determine the water content of each separately. LABORATORY OF PL.4NT CHEXISTRY BCREAUOF CHEMISTRY, WASHINGTON
~~
Xs a final experiment t h e moisture of t h e entire loaf as well as of different portions thereof was determined as follows: The loaf (which was a crust-covered one) was cut in half, and one half di\-ided into two quarters. T h e total moisture was determined on one quarter, and t h e moisture of the crust and of the crumb separately on t h e other quarter. From the remaining half loaf was cut a thick slice. as in our first experiment. and t h e different portions trimmed off as inrli-
A POLARISCOPIC DETERMINATION OF SUGAR I N
“CONDENSED MILK” B y R. 0. BROOKS Received September 20, 19!6
I n the legal analysis of “condensed milk,!’ two items are of paramount importance, vis.. t h e percentage of fat and t h e percentage of milk-solids. For the estima1 When t h e loaf is crust-covered, one quarter of i t , obtained by cutting t h e loaf in half crosswise and this half in two lengthwise, is sufficient t o represent t h e entire loaf. When t h e loaf lacks crust o n one side, by reason of having been baked in contact with another loaf, one half of t h e loaf is required for anal>-&.
Nov., 1916
T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY
tion of t h e f a t we have a n almost perfect method in t h a t of Gottlieb, as variously modified b y different analysts. For milk-solids in unsweetened condensed milk (formerly incorrectly called “Evaporated Cream”) it m a y be safely said t h a t t h e determination of total solids is sufficient. But in t h e determination of milk-solids in sweetened condensed milk, there is presented a far rnore difficult problem. The Official methods of t h e A. 0. A. C.’ (now being revised and published in t h e journal of t h a t association) have prescribed a determination of milk-solids in condensed milk b y the lengthy and very questionable method of estimating t h e fat, lactose, proteins (nitrogen X 6.38), and ash and taking t h e s u m of these. These four items do not comprize all t h e constituents of milk-solids ,and although the determinations of f a t and lactose may be quite correct, t h e estimation of proteins (N X 6.311) is a mere guess and t h e ash a mere residue of various mineral salts originally present, Sugar is determined in t h e Official methods by subtracting t h e above “milk-solids” from t h e total solids. T h e last item can be determined fairly closely and i t is obvious t h a t a far more logical and rapid method of estimating milk-solids in sweetened condensed milk is t o reverse t h e procedure and get t h e milksolids b y subtracting t h e sugar from t h e total solids. Various methods, gravimetric and polariscopic, have been proposed for t h e direct estimation of t h e sugar, b u t t h e problem cannot be regarded as satisfactorily solved hitherto. A tedious gravimetric method, utilizing copper reductions before and after citric acid inversion, h,Ls been tried out b y t h e A. 0. A. C., with some success, b u t of course a polariscopic method would be much more preferable in every way. Polariscopic methods have been proposed, including one b y Knight and Formanek in t h e January, 1916, issue of THIS J O U R N A L . T h e y have quite fully reviewed t h e faults of t h e past efforts along such lines and give a bibliography t h a t would be a waste of valuable space t o repeat here. Their own method seems somewhat lengthy and cumbersome t o the writer, who has used the simple method given below, in his consulting practice, for over a year, without his results failing t o agree with factory d a t a , even once. However, factory calculations on a large scale cannot be considered a n exact check; in fact, t h e only exact check is t o add an exact proportion of pure, dry sugar t o some unsweetened condensed milk and see how much t h e proposed method of analysis shows. TEST O F M € T H O D
Therefore pure granulated sugar was further purified, as described in revised Bulletin 107, 40, for standardizing saccharimeters, and t h e n thoroughly dried. A normal weight of this gave a reading of IOO on t h e sugar scale of the latest model of t h e Schmidt and Haensch sodium light polariscope. T o t h e appropriate quantity of a well-known brand of f r e s h unsweetened condensed milk a n d also t o some c a n n e d unsweetened milk (processed a t a higher temBureau of Chemistry, Bull 107, revised, U S Dept of Agr
1023
perature t h a n t h e fresh product) t h e above purified sugar was added, t o yield sweetened condensed milks containing exactly 45 per cent sucrose. On account of t h e lowering of the degree of concentration in commercial condensed milks (due t o overliberality in lowering t h e government standards) it has been t h e writer’s custom t o dilute 50 g. of t h e sample t o I O O cc., t h u s making t h e measuring and calculation of aliquots simpler and quicker. With aliquots representing 6.5 g. of each of the abovestandardized, sweetened condensed milks, the method of analysis gave, respectively, 45.07 per cent and 45.32 per cent sucrose. Using aliquots representing 1 3 g. (half-normal weight) of t h e two products, t h e method gave 45.I I per cent and 45.18per cent sucrose, respectively. Although t h e quarter-normal weight (6.5 g.) of t h e sweetened fresh condensed milk happened t o give the closest result ( 4 5 . 0 7 per cent), yet t h e writer is constrained t o favor t h e use of a A T / 2 weight (26 cc. or 1 3 9.) so as t o use smaller multiplying factors, as he is convinced t h a t t 4 e only possible error of t h e method is t h e personal one in taking the polariscopic readings. DESCRIPTIOh- O F THE M E T H O D O F A K A L Y S I S
Therefore t h e method as used is as follows: Weigh out exactly jo g. of t h e well-mixed sample, dilute with water t o exactly IOO cc. and carefully shake or stir until completely dissolved. Pipette1 exactly 26 cc. (13 g.) into a beaker, dilute with water t o about 40 cc. and add Fehling’s copper sulfate solution drop b y drop, stirring meanwhile, until t h e proteins and f a t are precipitated (about I . 5 cc. is sufficient). Filter on a paper similar t o t h e E. & A. qualitative analysis filter paper and wash t h e precipitate with water until t h e filtrate measures exactly I O O cc. Stir filtrate until of a uniform faint blue color and t a k e t h e direct reading in a 2 0 0 mm. tube of t h e polariscope, noting temperature, which should be between 2 0 and 30’ C. T o exactly 50 cc. of t h e filtrate add j cc. of concentrated hydrochloric acid, mix and allow t o s t a n d over night at t h e above temperature range. Add a few drops of phenolphthalein indicator solution, exactly neutralize with strong alkali solution and acidify with one drop of dilute (.IO per cent) hydrochloric acid t o discharge t h e red color. Make u p t o I O O cc., filter and t a k e t h e invert reading in zoo mm. tube a t same temperature as t h a t of t h e direct reading. Multiply t h e direct reading b y 2 and t h e invert reading b y 4 and calculate t h e sucrose b y Clerget’s formula, using t h e factor 141.7 , thus: I 00 (Direct reading-Invert reading) Sucrose = Temp. 141.7-2
T h e precipitate of proteins and fat on the filter paper (from first filtration) can be used for an estimation of proteins b y Leach’s method (drying, weighing, ashing and subtracting t h e ash and finally correcting 1 Shake or stir again just hefore measuring out t h e 26 cc. to avoid any formation of a cream layer. Of course a n exact 10 cc. portion of this diluted sample can be used for t h e Gottlieb fat determination and another 10 cc. portion for the determination of total solids and “ash.”
IO24
T H E J O L - R S A L OF I-YDCSTRIAL A S D ESGISEERIilrG C H E M I S T R Y
for f a t present) and it is probable that t h e fat could be determined on t h e dried precipitate b y powdering and extracting with ether in a Soxhlet apparatus, similar t o a method proposed b y A , E. Paul. Milk sugar (lactose) can be determined directly (by copper reduction gravimetric or by volumetric methods) on the filtrate before inversion, so we have here an outline for a “complete” analysis of sweetened condensed milk, using a t t h e most but three aliquots of the original diluted sample. The use of copper sulfate as a precipitant of proteins and mill K . \ X K L I S STRKET, S S W
YORK CITY
ESTIMATION OF SUGAR IN MEAT PRODUCTS, PARTICULARLY EXTRACTS’ By \V.
R. SXITH
Received July 1 2 , 1916
The best precipitants for t h e nitrogenous bodies in meats and meat extracts which interfere with t h e reduction of Fehling’s solution by sugar, are mercuric nitrate, mercuric acetate, and picric acid, followed b y phosphotungstic acid, with or without hydrochloric acid. For polarimetric x o r k t h e excess of mercury does not have t o be removed, b u t for copper reduction this is absolutely necessary. Irrespective of other qualities this fact makes t h e use of mercuric salts tedious and difficult. The removal of t h e excess of mercury is troublesome; although it has been performed with ease under certain conditions, which appear t o be distinct acidity, sufficient rapidity of the current of MzS, and not t o o concentrated solution, several chemists have found difficulty with it, especially when meat extracts containing high percentages of sodium chloride are being tested. If this p a r t of the clarification is not well done, t h e succeeding steps cannot be carried out successfully. This criticism applies particularly t o t h e nitrate of mercury; not only is t h e acetate of mercury more efficient as a precipitant, b u t the nitric acid greatly hinders the furmation of mercuric sulfide. For these reasons picric acid, when used in place of mercuric salts, not only- is easier of manipulation, but saves a very great proportion of the time required. Folin states,? “in t h e presence of copper, alkaline picrate solutions are not reduced b y sugar,” and this has been confirmed b y the experience of t h e writer. The sugar can, moreover, be estimated b y t h e picramic 1
2
Published by permission of the Secretary of Agriculture. J . A i d Chem., 22 ( I O I S ) , 327-9.
T‘ol. 8,K O . T I
acid reaction recently published by Benedict,’ Bernhard,2 and Myers EST13IATIOK O F S U G A R
I n this work the sugar was determined by reduction of Fehling’s solution and estimation of the copper in the precipitate by L o r ’ s iodide method. As described in a former paper,* difficulty is sometimes experienced (with t h e mercuric salts filtrate) i n filtering off the cuprous oxide, which comes down yellowand more or less soluble in water. Less difficulty has been found when picric acid is used The NunsonWalker method usually gives good results, especially when the percentage of sugar is high. Out of I j o tests of various methods the following are representative: PER CENT SCGAU FOUKD BY Bertrand 4.31 1.88 1 82
Munson-Walker PRODUCT Cured M e a t E x t r a c t . , . . . . . , . , , , , . , , , . . . . . 4 . 2 i Bouillon Cubes.. . , . . , ~, . . . , , . , , , , , , , , , . , 1 . 7 ; Extract from Spleens and Livers.. , , , , . , , . , I . 81
.
There are indications however, t h a t Bertrand’s method is more tolerant of impurities t h a n t h e MunsonWalker. The following tests were made on a single solution, clarified b y the picric acid method From extracts of beef: Percentages Sugar b y Bertrand method.. . , . . . , . . . . . , . , , . . . . . . . 0 . 0 9 0.13 0.39 Sugar by Munson-Walker: using 50 cc. of sugar solution 0 . 2 8 using 25 cc. sugar solution and 25 cc. w a t e r . , , . , , 0.20
The results b y Munson-Walker are not concordant and were affected by the amount of sugar solution taken. I n this instance the high figures were due t o a gummy residue which contained copper. The Munson-Walker method is superior in its definition of t h e time for bringing t o boiling, b u t Peters’ suggestion5 of a temperature limit is timely. The bulk of the reduction takes place before t h e mixture boils. On t h e whole, Bertrand’s method of reduction is preferred. As Bertrand’s tables did not reach below I O mg. sugar, t h e factor 0 . 4 9 was used t o convert copper percentages into sugar when necessary. R E M O V A L OF S I T K O G C X O I - s
norms
Bertrand’s method having been adopted as giving nearly accurate results for the purpose, various methods of removing t h e nitrogenous bodies which interfere were tested. Kearly all the work was done on meat extracts, which h a r e more of. the interfering bodies t h a n a n y other kind of meat product, and hence give the most severe tests of any method. Tt is well t o point out t h a t unclarified meat products give little or n o precipitation of copper because t h e cuprous oxide is held in solution b y t h e protein substances present. When these are partially removed a. point is reached a t which t h e holding of cuprous oxide in solution is reduced t o a minimum and high results are obtained, owing t o t h e presence of creatinin and similar substances which themselves cause a reduction of Fehling’s solution. While it cannot be said of a n y sample in advance which of these errors 1
8
4 5
“Estimation of Sugar in Blood,” J . B i d . Chem., 20 j1915), 67 G9. Chem. clbs., 10 (1916), 1230. .I. B i d . Chem., 24 (1916), 147. Jour. d s s o c . Oficial Agr. Chemists, 1, S o . 2 , .Aog , 1915 P P . 176 ~ 1 8 1 . J . A m . Chem. .SOL., 34 (19121. 930.
