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I N D UXTRIAL A N D ENGINEERING CHEMISTRY
meter. Finally. in ( e ) , the writers have already pointed out that the limit of elasticity appears to differ but little from the tenacity, or rupture limit, so that the resilience may be B2 €32 taken as 0.5 - = - where B = breaking load, and N = E 6n” rigidity, and could be expressed in ergs per cubic centimeter if absolute units are required. While these quantities can be determined in absolute units with our torsion instrument, this is not the case with the plunger type. It is obvious, however, that the plunger type can be calibrated on the torsion instrument by comparison of the results with the same gelatin jellies. Secondly, such elasticity determinations can he made with the same precision as viscosity. It seems to us that the use of the terms “jelly strength,” !‘jell consistency,” etc., in a
Vol. 15, N o . 6
vague and undefined sense should be abandoned, and that on account of this indefiniteness and the lack of investigation of systematic error, much of the work published on this phase of the subject requires careful revision. ADDENDUM Using jellies up to 8 per cent concentration, a comparison between the plunger type described here and our torsion instrument has been made for an ash-free gelatin and for a commercial gelatin. I n both cases the ratio” of the rigidities by the two instruments remained constant, the average for the ash-free gelatin (F3-14) being 43.0, for the commercial, 43.6. This apparatus constant, for the conditions used (depth of jell~75 5 em., ratio of diameters S 4 4 , should be a definite factor for converting jelly strengths into rigidities by the plunger method.
Changes in Powdered Rosin Stored in Closed Containers‘ By F. P. Veitch and W. F, Sterling BUREAU OF CHE‘MISTRY, WASHIXGTON, D. C .
PREVIOUS W’ ORK in which the quantity of Rosin powdered and stored in partly filled closed containers will change suficiently within one week. to show on careful analysis soap made from definite EGER2 found that quantities of lump rosin significantly lower acid and iodine numbers, higher saponification rosin in a thin and stearin of known soapnumber, and higher softening and melting points-and, inferentially. film exposed, to making value is compared higher specific grauity, increase in weight, and a greater proportion the air for 33 days inwith the quantity made of oxygen. creased in weight 1.58 per from a mixture of exposed Because of these facts samples should be prepared for analysis cent. Fahrion3 found that wowdered rosin and the only immediately- before the analysis is begun. Dowdered rosin exDosed for known stearin. Low yields i 4 mo. to the air and stirred were obtained with powfroni time to time differed widely in some of its constants from a portion of the same dered rosin that had been exposed to the air for 2 mo., while sample exposed at the same time in lump form, which had still lower yields were obtained with powdered rosin that not changed in that time. The acid number of the powdered had been standing for the same length of time over water. rosin had decreased from 159.0 to 151.2, the iodine number The authors assume that the oxidation of the rosin leads from 132.9 to 72.6, while the saponification number had to the formation of water-soluble compounds and that the increased from 165.8 to 174.7. He also found, by combus- soap-making value of the rosin is lowered more than protion, that the oxygen had increased from 12.7 per cent in portionately. the lump to 18.0 per cent in the powder, with proportionate EXPERIMENTAL WORKAT BUREAUOF CHEMISTRY decrease in hydrogen and carbon. He found that powdered In 1921, in reanalyzing within a few weeks a sample of rosin began to increase in weight in 2 days and gained 4.2 per cent in weight during 2 mo. Solubility in petroleum rosin, the writers found that its acid, saponification, and ether decreased with increase in oxygen content. When iodine numbers, and also the melting point of the powdered the exposed samples were dissolved in dilute alkali and samples kept in partly filled corked bottles, had all changed, shaken out with petroleum ether and salt, the lump gave while the unsaponifiable matter remained practically the same. The work of Fahrion and of Goldschmidt and Weiss 92.5 per cent and the powder 29.2 per cent soluble. shows the effect of exposing powdered rosin to the air for Palmer and Boehmer4 found that the extraction of rosin some time, but so far no reference to rapid changes or to from wood by petroleum solvents was complete. Schwalbe and Schultz5 found that the longer pine wood changes within a closed receptacle such as is generally used was kept, particularly in the form of sawdust, the smaller in the laboratory for storing samples for analysis, has been was the quantity of resin that could be extracted, even by a found. This fact, while interesting in itself, explained in part, though not entirely, the wide discrepancies between the series of different solvents used successively. Goldschmidt and Weiss6 found that the soap-making value constants of rosin reported by different analysts and also the of exposed powdered rosins”was from 2 to 5 per cent less than decided differences heretofore found between the different that of lump rosins as determined by the stearin method,7 grades of rosin, differences which were not confirmed by the Bureau of Chemistry in careful work on the constants of 1 Presented before t h e Division of Industrial and Engineering Chemistry rosin, in which samples of known origin and grade were used at t h e 64th Meeting of the American Chemical Society, Pittsburgh. P a , and the sample for analysis taken from the lump at the time September 4 t o 8, 1922 of analysis. aChem. Rev F i t t - H a m - I n d , 6 (1898), 236. I b i d . , 22 (1915), 97. The fact that the constants of rosin do change after the 4 THISJOURNAL, 8 (1916). 695 rosin is powdered having been fully established, it evidently 6 Z . angew. ChPm., 3 1 (191S), 125 becomes important to know how soon these changes take 62.deut. bl- Felt-Ind., 4 1 (1921), 147. place and the rate a t which they take place under ordinary 7 Seqfenfabr , 39 (1919), 49.
vv
8
I
I N D U S T R I A L A N D ENGINEERING CHEMISTRY
June, 1923
analytical conditions. To this end 50- to 100-g. samples of rosin were finely powdered in a porcelain mortar and placed in wide-mouth bottles, which were filled about threefourths full, and stoppered. The bottles were kept closely stoppered and exposed to the diffused light of a rather dark laboratory. They were not opened or agitated except when portions were withdrawn for analysis. The samples were analyzed as soon as prepared and then a t intervals, as indicated in Table I. The work was all done in duplicate or triplicate, and the greatest care exercised to do it under exactly the same conditions. All melting-point determinations were made in a capillary tube emersed in a glycerol bath, and the same thermometer was used in all cases. In determining iodine numbers exactly 0.15 g. of sample and 30 cc. of iodine solution were allowed to stand exactly 1 hr. at 21Oto 23' C. in the dark, the flasks being shaken four times for a period of 0.5 min. each. In determining acid and saponification numbers, the same quantities of sample, solvent, and solution were used in all cases.
RESULTS The results of this work are given in Table I. TABLE I-CONSTAiiTS
BOTTLED,POWDERED ROSINS ANALYZEDAT DIFFERENTTIMES UnsaAcid Saponi- Iodine MELTINGPOINTponiNo. fication No. Softens Fluid fiable When Analyzed Grade (Direct) No. Wijs C. C. % 50.1 62.4 6.9 At s t a r t WW 1 6 4 . 5 1 7 5 . 3 229.0 After 1 w-k. \V\V 160.9 179.0 214.9 51.8 65.6 6.9 OF
4 t start After 1 wk.
K K
166.9 164.5
174.1 178.5
225.2 208.9
54.8 57.2
67.8 ,71.3
5 5 5 5
At start After 1 wk.
F F
160.9 155.3
171.4 175.6
216.8 192.4
59.8 63.1
70.6 74.6
7 9
At s t a r t WXX' 1 6 3 . 1 Artrr 1 wk. W W l5S.O After 2 wks. \\7W 156.0 Aiter 3 wks. WW 1 5 5 . 3 After 6 wks. WU' 1 5 5 . 0 Total change -8.1
173.2 228.1 50.9 63.8 53.2 68.2 214.0 178.1 57.7 71.8 180.2 205.5 198.3 59.7 72.7 181.5 75.1 175.9 62.8 181.6 +11.9 t 1 1 . 3 t 8 . 4 -52.2
7 4 5
A t start M-1 After 1 wk. M-1 After 2 wks. M-1 After 3 wks. M-1 After 6 wks. M-1 Total change
164.2 158.9 156.3 155.4 154.9 -9.3
174.1 224.1 53.6 65.2 213.2 54.8 69.9 179.4 202.2 60.2 73.7 181.4 197.1 61.7 74.7 182.7 175.5 63.6 76.1 183.0 + 8 . 9 -48.6 f l O . 0 $10.9
7 2 7 2
A t start M-2 After 1 wk. &I-2 After 2 wks. M-2 After 3 wks. M-2 After 6 wks. M-2 Total change
164.9 160.6 158.0 156.9 156.7 -9.2
176,O 224.7 53.9 65.0 211.0 55.3 70.2 179.3 200.5 60.8 71.8 182.5 195.6 61.9 73.1 183.3 174.2 63.7 76.0 183.5 + 7 . 5 -50.5 f 9.8 + l l . O
At start H-1 After 1 wk. H-1 After 2 wks. H-1 After 3 wks. H-1 After 6 wks. 13-1 Total change
164.3 161.4 158.4 157.1 156.9 -7.4
215.7 59.3 176.2 198.8 62.2 179.0 190.2 64.5 182.1 183.2 65.9 183.0 167.2 69.4 183.1 +lO.l + 6 . 9 -48.5
70.7 74.4 76.9 77.3 80.1 9.4
8 8 8 8
At start H-2 After 1 wk. H-2 After 2 wks. H-2 After 3 wks. H-2 After 6 wks. H-2 Total change
168.3 166.0 164 1 163.*1 163.0 -5.3
179.0 220.6 210.2 181.1 201.1 182.8 196.3 184.0 173.3 184.1 + 5 . 1 -47.3
70.8 74.3 76.2 77.9 80.3 9.5
8 8 8 8
At. start E After 1 wk. l? After 2 wks. E After 3 wks. E After 6 wks. E Total change
161.7 172.8 214.0 107.5 158.3 176.3 189.2 156.5 178.4 181.5 155.1 179.8 154.9 180.0 163.3 -6.8 + 7 . 2 -50.7
71.9 75.4 77.2 78.4 51.2 9.3
9 5
59.8 61.9 64.8 65.8 68.7 8.9
+
61.2 64.2 66.4 67.5 70.1 4- 8 . 9
7 5 7 5 .
a
7 2
.
a
7 8 7 s 7 8 a
3 4 3 3 a
0 0 0 0Q
+
+
9 4 9 4 a
XOTE All values except melting point were r u n in duplicate, which differed in all cases by less t h a n 0 5 O C. T h e melting point was determined in triplicate, which agreed within 1' C Only averages a r e given. a N o t enough sample t o determine.
It vITas also found that the solubility of the powdered rosin alcohol (1 part g j per cent alcohol to 1 part of the rosin) had not decreased. These results show that certain of the so-called constants
111
577
of powdered rosin undergo pronounced changes within a short time, even when in partly filled corked bottles; that while the rate of change slows down considerably after the first week, the change continues a t a significant rate for a t least 3 wks., after which only the iodine number and the softening and melting points continue to change appreciably. It is clear that changes in these have not ceased in 6 wks. At the expiration of 6 wks. the changes were found to be a decrease of from 5.3 to 9.3 in acid number, an increase of from 5.1 to 8.9 in saponification number, a decrease of from 47.3 to 52.2 in iodine number, an increase of from 8.9 to 11.3 degrees in melting point. Although there is some indication that these changes are greater in the high- than in the lowgrade rosins, the evidence on this point is conflicting, except as to softening and melting point, where, because of the higher temperature at which the lower grades are made, the difference would not be expected to be so great as with the highgrade rosins.
NATUREOF CHANGES The writers have not yet had an opportunity to study the nature of the changes which take place in powdered rosin. That oxidation takes place may be accepted without question, in view of Fahrion's results. They are inclined to think, however, that this is not the sole change that takes place. Fahrion3 states that during exposure of powdered rosin to the air, peroxides are formed by oxidation at the double bond, and that these peroxides are unstable and readily undergo a rearrangement. The rearrangement product can be changed to the anhydride of oxyabietic acid by cleavage of water, by heat, or by chemical treatment. He also found that a certain quantity of anhydride mas formed without the assistance of artificial agencies. On the other hand, it must be remembered that some anhydride, arising from the methods of preparation, may be present in the rosin from the first. Fahrion further claims that two oxyabietic acids are formed on exposing powdered rosin to the airfirst a dioxy acid and then a tetroxy acid-but that the conversion to the tetroxy acid may not be complete even after 22 mo. exposure of the rosin, as shown by the iodine number of around 50 which the exposed material still showed. Ellis and Rabinovitzs found that the anhydride did not readily neutralize a cold, dilute, aqueous solution of caustic alkali on titration, but on the other hand did neutralize a cold, dilute, alcoholic solution of caustic alkali. They obtained the anhydride by heating rosin a t 300" C. Heating was continued until the acid number determined by titrating a solution of the material in benzene or ether with aqueous caustic potash was 20. It was found, however, that when titrated with alcoholic caustic potash the acid number was but little below the normal value for rosin.
CONCLUSION It is clear from the authors' results that in determining the constants of rosin, or, in fact, in making any other tests of rosin, a sample which has been powdered for but even a few days cannot be used. It seems probable also that the 1 1ide variations obtained at times bv different analysts working on the same samples 01 by the Same analyst on different grades of rosin are due in part to the use of samples which had been powdered for a longer or shorter time. Furthermore, in the determination of rosin in shellac or other materials which are ground or powdered before analysis, the possibilities of the changes shown above must be taken into Consideration. 8
THISJ O U R N A L , 8 (19161, 406
