T H E JOURNAL OF INDU8TRIAL A N D ENGINEERING CHEMISTRY
210
Vol. 14, No. 3
Leavens: Their Action and Measurement”z By Clarke E. Davis3 and Donald J. Maveety RESEARCH LABORATORY, NATIONAL BISCUIT CO., NEWYORK, N .
Y.
EAVENING is the process of forming in a dough question existed as to the ultimate end of the reactions. bubbles of gas which escape in baking and leave a The purpose of the writers was to determine the weight of light and porous texture in the baked product. A sodium bicarbonate or carbonate which would react with a leavening action takes place when a carbonate or bicarbon- given weight of phosphoric acid or primary calcium phosphate. ate is acted upon by an acid or acid salt. The simplest EXPERIMENTAL form of leavening is by the aid of steam. A fairly good TITRATION-Direct determinations of acidity by titration result is obtained by baking a mixture of flour and water, where the texture is produced by the escaping steam. The with standard sodium hydroxide gave the following results, most familiar type of product leavened in this way is in percentages of the acids involved: army bread or pilot bread. Per cent Soda (sodium bicarbonate) through the agency of heat is a Tartaric acid (Phenolphthalein). ............... 99.6 Cream of tartar (Phenolphthalein). ............. 100.4 simple form of leavening agent and may be used alone in Phosphoric acid (Methyl orange). .............. 50.0 quantities which will not leave the bad aftertaste due to excess soda. This amount is about 1.5 lbs. sodium bicarbonate It wm found impossible to analyze primary calcium phosphate per barrel of flour. Ammonium bicarbonate (NHdHCOa) by titration. and the so-called ammonium carbonate, a mixture of the EILECTROMETRIC TITRATION-The acid reacting substancw bicarbonate and the carbamate (NH&COa and NH~CO~NHZ),were titrated electrometrically with standard sodium hydecompose with heat, liberating ammonia gas and carbon droxide in order to discover any possible irregularities with the dioxide and thus giving a double leavening value. More different acids. The method and apparatus used were those complex mixtures are represented by sodium bicarbonate with described by Beans and Oakes.’ The apparatus wm standprimary phosphates of sodium or calcium, phosphoric acid, ardized by titration of 0.1 M hydrochloric acid with 0.1 M tartaric acid, cream of tartar, sodium aluminium sulfate, etc. sodium hydroxide. (See Fig. 1.) Measurements were made Great confusion prevails as to the chemical reactions with the same alkali against tartaric acid, cream of tartar, which occur when such chemicals are mixed. Hart4 gives phosphoric acid (commercial), and primary calcium phosthe following reactions: phate with the results indicated in Figs. 2, 3, 4, and 5. The 3 CaH4 (P04)~f 8 NaHCOs = 8 COZf 8 HzO f Car (PO&. 4- curves represent simple electrometric measurements of 702 672 352 144 310 hydrogen ion designed for comparison with the acidity 4 NazHPO4 shown by indicator titration. The abrupt changes in the 568 curves correspond to the sudden changes shown by indicators KHC4H406 f NaHCOa = COS HzO f KNaC4H406 and represent the end-points of the displacement of a first or 188 84 44 18 210 second hydrogen. The middle points of the upward breaks represent these values: Leach6 gives the following reactions: Per cent CaH4(PO& 4-2 NaHCOa = 2 COa 4-2 HzO fCaHPO4 fNaaHPO4 Tartaric acid.. ............................. 99.8
L
+
234
168
88
36
136
142
Cream of tartar.. ........................... Phosphoric acid.. Primary cdcium phosphate..
......................... .................
+
99.4 62.7 86.8
H2C4H4O6 2 NaHCOs = 2 COZf Na~C4H406.2HzO 150 168 88 230
GOz EvoLvm-In order to determine directly the weight ratios existing between the carbonate and the acid or acid salt, the weight of carbon dioxide given off by the reactions Patten6gives the following reactions: was measured by means of an absorption train. The reacting 3 CaH4 (P04)~f 4 NaHCOa = 4 COz f 4 HzO f Cas (Po&f materials were weighed into an Erlenmeyer flask, Coyfree 702 336 176 72 310 water was added, and the reaction carried to the end by the 4 NaHzPO4 aid of heat. Sodium carbonate was used because sodium 480 bicarbonate breaks down with heat. 3 CaH4 (PO4), 8 NaHCOa = 8 C02 f 8 HzO Car (PO& f Table I shows the results obtained by actual carbon dioxide 702 672 352 144 310 measurements.
+
+
4 NazHP04 568
T A B LI ~
Measured Theoretical
NaaCOa CO: cor Acid Grams Grams Grams Grams In order to determine the weight ratios of sodium bicar0.3516 0.1441 0.1460 Tartaric............. 0.5000 bonate and the different acids and acid salts, the chemical 0.3500 0.1440 0.1454 Cream of tartar., ..... 1.2370 1.000 0.3225 0.3284 Phosphoric.. ......... 1.3878 reactions must be definitely known. In the case of tartaric acid and cream of tartar the reactions needed to be checked Tartaric acid and cream of tartar were mixed with sodium for the purposes of the present investigation. In the case carbonate in stoichiometric proportions. In the case of of phosphoric acid and primary calcium phosphate ‘some phosphoric acid, the carbonate was added in excem. These 1 Presented before the Division of Agricultural and Food Chemistry results show the reactions in the cases of tartaric acid and at the 02nd Meeting of the American Chemical Society, New York, N. Y., cream of tartar to have been direct neutralization of all the September 0 to 10, 1921. hydrogen ion of the acids. (See equations in introduction,) Published as Contribution No. 3 from the Research Laboratory of the I n the case of phosphoric acid, two-thirds of the hydrogen National Biscuit Co. 8 Consulting Chemical Engineer, National Biscuit Co. ion were neutralized and there action came to an end with the 4 “Leaveqing Agents,” 52. formation of NazHP04, disodium phosphate: 6 “Food Inspection and Analysis,” 4th edition, 349. f
6
J . Assoc. Oficia? Agr. Chem., 2 (1917),227.
7
J . A m Chcm. Soc , 43 (1920), 2116.
THE JOURNAL OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY
Mar., 1922
211
11.0
0.5147Gtl. CREAM OF TARTAR, IN 2 0 0 BOILED ~ ~
10.0
D ISTJLLE D WATER,
9.0
BY MEANS OF H2- ELECTRODE - AT 25°C
8.0
7.0
6.0
5.0 4.0 3.0 2.0
0 5
IO I5 "0
3 0 35 40 45 50 0
25
5
IO 15'20 25 /30
35
40
45 5 0
0
5
IO 15 '30 25 30 35 40 45 5 0
from the acid phosphate used, and sodium carbonate was in excess. This last experiment gave carbon dioxide corresponding to the reaction which has Ca3(PO&, neutral calcium phosphate, and Na2HP04, disodium phosphate, as its endproducts, and did not stop with the formation of CaHP04, secondary calcium phosphate.
+ 4 N a ~ C O 3 z - COZ 4
3 Ca(HzP04)~ 702
424
176
+ 4 HzO + Cas(P04)~ + 4 NazHP04 72 310 568
4.0-
3.02.00
5
HsP04 98
IO 15 20 25 30 35 40 45 50 0 5
+ NazCOs 106
IO 15 20
+ HzO + NazHPO4 18 142
:J_ COZ 44
Converted to bicarbonate, this equation becomes HsPOl 98
+ 2 NaHCOa 168
J7
2 COZ4-2 HzO 4-NazHPO4 88 36 142
When primary calcium phosphate reacts with sodium carbonate, different results are obtained, depending on the ratio of acid to base and on the time of the reaction as indicated in Table 11.
25 30 35 40 45 50
Converted to equation reads
bicarbonate,
the
3 Ca(HzP04)2+ 8 N a H C O a z 8CO? 702 672 352
+ 8H20 + Cas(P04)~ + NazHPOd. 144 310 568
In order to determine whether Cas(PO& or CaHP04 is formed in a solution which is not strongly alkaline, sodium carbonate and primary calcium phosphate were used in proportions to give the reaction Ca(HzP04)~f Na2COs;C ' Oz 234 106
f HzO 44
18
+ CaHP04 4-NazHPO4 136 142
or, converted to bicarbonate,
TABLEI1 Primary Calcium Phosphate Grams 1.000 1.000 1.000 1.000
NarCOs Grams 0.4716 0.4718 1.000 1.000
cot
Produced Grams 0,1755 0.1920 0.2076 0.2170
Time Hrs. 1.0 1.5 1.0 2.5
Theoretical Cor Grams 0.1957 0.1957 0.2170 0.2170
In the fkst two experiments of Table I1 the theoretical carbon dioxide was calculated from the amount of sodium carbonate used, and an excess of acid phosphate was present. In the last two the theoretical carbon dioxide was calculated
NazHPOl 142
and the carbon dioxide was collected and weighed. The material remaining in the reaction flask was filtered and separate determinations with additional sodium carbonate were conducted on filtrate and precipitate. If carbon dioxide were developed by the action of the solid residue, it would prove that material to be not Cas(POa)zbut CaHP04. The results are given in Table 111.
