Mar., 1912
T H E JOURiZrAL OF ~ I V D L - S T R I A LA N D E N G I N E E R I N G C H E M I S T R Y .
results than can be obtained by the direct method as i t is commonly practiced. CONCLUSIONS I . Gluten as i t is ordinarily prepared has a variable nitrogen, ash, starch and moisture content. 2 . The peculiar copper reduction resulting from adding the filtered extract from hydrolyzed gluten by acid is undoubtedly due t o some other substance than starch or sugar. 3. An average of about 7 j per cent. of the total nitrogen of flour enters into the crude gluten. 4. Glutens obtained from low-protein flours are not necessarily any richer in nitrogen, more free from ash, etc., than glutens derived from medium- or highprotein flours. 5 . The reason why low-protein flours yield much lower per cents of gluten than medium- or high-protein flours may be attributed to the scattering of such glutens, resulting in mechanical loss. By blending such flours with strong gluten flours, results in yields comparable t o those obtained for medium- and highprotein flours, AGRICULTURAL EXPERIMENT STATION, PULLMAN, TVASH
A COMPARATIVE STUDY OF METHODS FOR THE DETERMINATION OF HARD AND TOTAL SOFT RESINS IN THE HOP. By H. V. TARTAR A N D C. E. BRADLEY. Received October 17, 1911.
Previous t o taking up some chemical investigations at this laboratory i t became necessary t o devote some time t o a study of methods for the determination of hard and total soft resins in the hop. Some very interesting results have been obtained which the authors think may be of value, especially t o those connected with the brewing industry where the correct valuation of hops is of considerable moment. The results given may also be of some use t o the work recently undertaken b y a Committee of the International Barley and Hop Prize Exhibit a t Chicago for the establishment of definite hop standards. Previous investigations have shown that there are a t least three so-called resins which are constituents of the hop cone, one “ h a r d , ” tasteless resin and two “soft” bitter resins, Although a considerable amount of research has been done on the nature of these substances and their function in brewing, much is still obscure and in doubt. I t is generally agreed, however, t h a t the hard resin is of little or no commercial value, while investigations indicate t h a t the major part of the real brewing value of hops lies in the soft resins, thus making their estimation of considerable importance. I n this study two different methods for the determination of both hard and total soft resins have been given a test: Briant and Meacham’sz method and Siller ’s* method. The original volumetric method
of LintnerI and .the modified Lintners method for total soft resins have also been studied. Although the original Lintner method has been shown to be inaccurate we have included i t in this study because we have found from our correspondence that this method is still employed in a few instances. A method devised by us is given and the comparative results are reported. We have had good success in the use of this method, and while not claiming originality for the basic principles involved, we believe it overcomes some of the objections t o present methods. For .convenience i t is here designated as “authors’ method.” Not all of the methods for the estimation of hop resins are given. but we believe all have been included that are receiving any extensive use. X‘I ETH 0D S
J . Fed. I m t . Brewtng, 3, 233 (1897).
2 Ztg.
U n f e r s w h .Nahrwzg-Genuss.. 18, 241.
.
In all the methods which have been devised for the determination of hop resins, the separation of the soft resins from the hard resin is dependent upon the ready solubility of the former in petrolic ether, the latter being practically insoluble in this solvent. The extraction of total resins from the hop is effected with ordinary ether. Briefly stated, the methods compared are as follows : Briant and Meacham’ss Method.-About four grams of hops are placed in a Soxhlet extractor and extracted for twenty-four hours with petrolic ether (boiling point s o o (2.). After the extraction is completed the extraction flask is disconnected from the apparatus and its contents filtered while hot through a small filter paper into a tared wide-mouthed flask; the filtrate is then gently evaporated. The final drying operation is completed by placing the flask on its side in a hot water oven, where i t is maintained a t a temperature slightly above the boiling point of the ether until its weight is constant. The extract thus obtained is the total soft resins in the sample. The hops left in the extractor from the petrolic ether extraction are next extracted with ordinary ether for 1 2 hours. The ethereal extract is then filtered into a tared flask, dried and weighed as in the previous extraction, the residue obtained being estimated as hard resin. Sillers Method. Soft Resins.-A ten-gram sample of hops which have been ground through a small meat grinder is placed in a Soxhlet extractor and extracted with petrolic ether (boiling point 30-40 O C.) for 8-10 hours. The petrolic ether extract is then evaporated in vacuo on a water bath a t 40’ C. until all of the solvent is removed. The residue is then taken up with methyl alcohol t o separate the wax present, filtered and made to I O O cc. volume. A I O cc. aliquot (equivalent t o I gram of hops) is placed in a weighed flask and the alcohol is then completely evaporated in a drying oven a t 80’ Z t v . Ges. Brawesen, 21, 407. Chem. Z t g , 32, 1068; 0.Neuman, Wockonschrafffur Brauori, 1910. 8 L O G . cit.
1 1
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C., the evaporation requiring 4-5 .hours. The residue obtained is estimated as total soft resins. Total Resins.-A ten-gram sample of ground hops is placed in a Soxhlet extractor and extracted 8-10 hours with ordinary ether. The ethereal extract is then evaporated i n vacuo a t 40° C. until all of the ether is removed. The residue obtained is taken u p with methyl alcohol t o separate the wax, filtered a n d the filtrate made t o I O O cc. volume. A I O cc. aliquot (equivalent t o I gram of hops) is placed in a weighed flask, evaporated and weighed in the manner used in the determination of total soft resins, the residue obtained representing the total resins in I gram of hops. The hard resin is estimated b y difference between the amounts of total resins and soft resins. Lintner’s‘ Volurnetric Method f o r Soft Resins.-This method is based upon the fact t h a t the two bitter substances commonly called soft resins react in solution as monobasic acids with alkalies. A ten-gram sample of hops is introduced into a 500 cc. flask having also a mark a t 505 cc.: 3 5 0 cc. of light petrolic ether (boiling point 30-50’ C.) are added and the flask attached t o a reflux condenser. The flask is then heated on a water bath and the extraction continued for eight hours. When cooled t o 17.5O C. the liquid is made up t o the 505 cc. mark, well shaken and then filtered. One hundred cc. of the filtrate are mixed with 80 cc. of alcohol, I O drops of phenolphthalein solution (I :I 00) added. and then titrated with a tenth-normal solution of potassium hydroxide until the red tint just appears. A blank experiment is made t o ascertain the amount of potassium hydroxide neutralized b y the mixture of alcohol and petrolic ether. The number of cc. required for the titration multiplied b y the factor 0 . 0 4 (the molecular weight of the bitter substance taken as 400) represents the amount of soft resins in the aliquot . Modified Lintner Method2 f o r S o f t Resins.-The determination is carried out in the same manner a s ‘ i n the original Lintner method except t h a t the hops are ground previous t o the extraction. Authors’ Method.-Ten grams of hops are placed in a Soxhlet extractor and extracted with ether for 8-10 hours. The ethereal extract thus obtained is filtered and the filtrate made to zoo cc. volume. Total Resins.-One hundred cc. of the ether solution (equivalent t o 5 grams of hops) are placed in a 250 cc. Erlenmeyer flask and nearly all of the ether removed b y distillation on a water bath at about 40° C. The last portion of the ether is completely removed b y drying in a vacuum desiccator at room temperature. The residue remaining is then taken u p with alcohol t o free the wax, filtered and the filtrate made t o I O O cc. volume. A 20 cc. aliquot (equivalent t o I gram of hops) is transferred t o a tared beaker and the alcohol removed b y evaporation in a vacuum oven a t s o o C. t o constant weight. The
’
LOC.
cit.
’Char.
Zfg..
32, 1068; 0.Neuman, W o c k c h r i f t
fur
Braueri, 1910.
Mar.,
1912
residue thus obtained is the total resins in one gram of hops. Total S o f t Resins.-The remaining I O O cc. of the original ether extract are transferred t o a zoo cc. Erlenmeyer flask and the ether nearly removed by distillation a t low temperature, the last portion being removed b y evaporation in a vacuum desiccator a t room temperature, The residue is taken up with about I O O cc. of petrolic ether (boiling point 40-45’ C.). The residue is worked u p in the solvent with a glass rod and then let stand a short time t o effect the complete solution of the soft resins in the solvent. The hard resin is then removed b y filtration. The petrolic ether is removed from the filtrate in the same manner as the ether in the first part of the determination. The residue is taken up with alcohol t o remove wax, filtered and the filtrate made t o I O O cc. volume. An aliquot of 20 cc. (equivalent t o I gram of hops) is transferred t o a tared beaker and evaporated and weighed as under the determination of total resins. The hard resin is estimated b y difference between the total resins and soft resins. E X P E R I M E N T A L PART.
Five samples of Oregon hops of the 1910 crop were analyzed, using each of the different methods given above. Sample No. I was a n air-dried sample and Nos. 2-5 were commercial samples which had been kiln-dried. In each instance the extraneous matter, such as leaves and stems, was separated, only the whole unbroken cones being used for the determinations. The results of the analyses are given in Table I. The table shows a wide variation in the results obtained b y the different methods. Siller’s gives extremely high results for soft resins while Briant and Meacham’s and the original Lintner method show very low results. The amount of soft resins obtained b y Lintner’s modified method and the authors’ method agree fairly well. Briant and Meacham’s method shows very high results for hard resins while Siller’s and the authors’ give much lower amounts. The low results for soft resins obtained b y the Briant method and the original Lintner method are due t o the fact t h a t the extraction of the soft resins is not complete. The lupulin granules of the hop cone must be well broken up before the soft bitter resins can be completely extracted with petrolic ether. Siller~has already pointed out this fact and has suggested the grinding of the hop previous t o the extraction as a means of overcoming this defect. Grinding b y means of a meat grinder or with sand in a n ordinary mortar has been found satisfactory for the preparation of the samples for extraction. When the meat grinder is used, the sample is taken after the material has been ground. The high percentage of hard resin secured b y Briant and Meacham’s method is due t o the presence of soft resins left from incomplete extraction with
’
L O C . cat.
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TABLE I.- -TIIF.RESIXCOSTEXT O F OREGONHOPSBY DIFFEREST METHODS. Sample 2. Sample 3. Sample 4.
___--
-
Sample 1 .
~-
Soft Total resiu. resin. Per Per cent. cent. 8.011 9 . 0 9 17.09 2.89 20.07 22.96 1.9i 16.75 18.73
IIard resin Per cent..
Method. Briant and 3 I e ~ c h a n i ' s . , Siller's. . . . . . . . . . . . . . . , Authors'. . . . . . . . . . . . . , . , , Lintner's original. . , . . , . . . Lintner's modified. . . . . . . .
Hard Soft Total resin resin. resin. i'pr Per Per cent. c- the f(.,llon-ipg cs:-icii::icnt : Six c # T dificirent size; n-ere selc,ctecl frriln cncl: t'71-c f e r m t coni ni crc i a 1 s:i nil 3 I (T. t 11c i r TI-c i E-?t t n l i cn , nt i c 1
- _ - _ _ - A _ _
Hard re4in Per cent.
- . ~
Soft Total resin. resin. Per Per cent. cent
1 1 ,54 8 S 4 20.38 2.52 21.49 24.01 1.52 18.50 20.02 5.20 19.32
Sample 5.
,____.___
->
Hard Soft Total resin. resin. resin. Per Per Per cent. cent. cent. 11.37 8 .59 19.96 1.93 20.36 22.89 1.79 17.29 19.08 6.80
18.00
Hard Soft Total resin. resin. resin. Per Per Per cent. cent. cent. 7.54 8.68 16.22 1.33 17.01 18.34 1.89 13.73 15.62 6.40 13.20
thv amount of total resin in each cone estimated by extractin,y n-ith ether and drying t o constant weight iiz ;'ac21Li a t .yoo C. The results are tabulated in Table 111. T h e diffcrcnces between the maximum and minim u m pcrccntages of total resin in the cones from eac?i of the samples are 3 . 8 7 , 3 . 8 2 and 6 . 8 8 per cent. respcctivel!-. 'The most notable difference is in cf-mias J I and I11 of sample No. 3 where two cones oi i)racticnll>-the same weight differ 6 . 8 8 per cent. tent from these results t h a t samples of at lrast I O grams n-eight must be used for the determination o f resins, and where accurate results are tlesircd i t has been found advisable t o make triplicatc tfeterminations. The determination of hard resins, furthermore, should be made on the same wiiiIjlc as used for soft resins. 1,intner's modified volumetric method has been fimnd t o give fairly good results. We believe i t t o he the best av-ailable rapid method for the estimation of soft resins suitable for commercial use. Gravimetric and volumetric determinations made on aliquots from the same solution of soft resins show t h a t the volumetric method does not always agree with the gravimetric, often giving results which are someivhat higher. The comparative results of a number of tleterminations made in this manner from different samples of hops are as follows: Soft resins. Authors' gravinietric method Per cent 17.29 17.75 14.44 16.45 16.64 15.52 16.13 15.58
Soft resins, Lintner's volumetric method. Per cent.
17.30 18.20 15 .00 17.70 17.00 16.70 16.00 16.20
'&
(,?
' T h e sliyh tly hiEher results xivcn b y the volumetric tietcrminntions arc lierhaps tluc to the use of the .tiiphrr . ilf thc rnc~lecularn-eights of the different soft resins for niaking thc calculations. IIrT-ing tlic resins a t as high a. temperature as 8 o o
Sample . . . . . . . . . . . . . . . . . . . . 2.. . . ..... .
3
.
0.2312 20.74 0.3753 21.57 0.2;(18 1s.3.5 0 . 1 ~ 0 0 18 SS 0.1622 19.05 0.1322 17.70 21.57 0.2513 18.74 0.3105 ?O.O3 0.3410 18.59 0.2058 22 41 0.1193 21.43 0.1870 20.59 22.41 0.4943 20.00 0.3075 23.22 O . A O 3 j 16.34 0 3630 18.07 0 3335 19.88 0,2064 18.12 23.22
17.70 19.38 18.59 20.29 16.34 19.27
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C. is open t o objection for two reasons: first, the resins turn brown a t this temperature and undoubtedly there is some change in composition; second, a constant weight cannot be obtained. When the resins are dried in vacuo there is no evidence of much change in composition and when. completely dried there is practically no change in weight. Great care should be taken in securing petrolic ether of suitable quality for the extraction of the soft resins. The practice in this laboratory is bo make two distillations, starting with the commercial product sold b y dealers (boiling point 40-60’) and each time taking the fraction distilling over under 45 O C. Acknowledgment is due Mr. B. Pilkington for valuable assistance given in making some of the analytical determinations given in this paper. CONCLUSIONS.
I . A comparative study has been made of some of the present methods used for the determination of hard and soft resins in the hop and their defects pointed out. 2. A method has been proposed b y the authors which they believe overcomes some of the objections to present methods.
LABORATORY AGRICULTURAL EXPERIMENT STATION, CORVALLIS,OREGON.
THE CHEMISTRY OF ANAESTHETICS, IV: CHLOROFORM.1 BY
CHARLES
BASKERVILLE AND W. A. HAMOR.
The career of chloroform has been since its, discovery, b u t especially since os a n anaesthetic, The reasons for apparent in this paper. The report of this investigation divided as follows:
chequered ever it has been used this are made has been sub-
Mar., 1912
in Chloroform. 6 . The Detection of Acetone in Chloroform. 7 . The Detection of Methyl Alcohol and other Methyl Compounds in Chloroform. 8. T h e Detection of Ethyl Ether in Chloroform. 9. T h e Detection of Acetaldehyde in Chloroform. I O . T h e Determination of the Acidity of Chloroform. 1 1 . T h e Decomposition Products of Pure Chloroform. I r ( a ) . T h e Detection of Carbonyl Chloride. I I ( b ) . The Detection of Hydrochloric Acid. II(C). The Detection of Chlorine. 1 2 . T h e Detection of Chlorine Substitution Products. I 2 ( a ) . “Chlorinated Decomposition Products. ’’ I 2 (b) . T h e . Occurrence of Ethyl Chloride i n Chloroform. 12(c). T h e Occurrence of Ethylene Chloride in Chloroform. I z ( d ) . T h e Detection of Carbon Tetrachloride. 13. Scheme for the Examination of Chloroform for Anaesthetic and Analytical Purposes, with Particular Reference to the Detection of Avoidable Impurities. 14. T h e Degrees of Purity of American Chloroforms.
I n this paper the grades of chloroform have been discriminated in accordance with the following classification, which the authors propose as a basis: A. Pure Chloroform.-Absolute chloroform-chlo~oform free from alcohol and all impurities B. Anaesthetic Chloroform.-Chloroform complying with the pharmacopoeial requirements. Such chloroform contains ethyl alcohol (up t o I per cent.) and small amounts of water. C. Commercial Chloroform.-Chloroform which contains at least 99 per cent., b y weight, of absolute CHCl,, b u t which may contain small amounts of d l organic impurities.”’ D. All other grades of chloroform sliouid be classed as impure commercial chloroform. E. The purity demanded of laboratory chloroform, or chloroform intended for analytical purposes, is entirely dependent upon the purpose for which it is intended. For ordinary reagent purposes, the grade specified under anaesthetic chloroform is suitable, and in general may be said t o answer all such purposes; but in special cases pure chloroform may be required, and, when this is the case, i t should always be prepared immediately before use, according t o a method t o be described in Section V, I , A of this paper.
I . HISTORY. 11. U S E S . 111. MANUFACTURE: I . From Ethyl Alcohol. 2 . From “Methylated Spirit.” 3. From Acetone. 4. From Methane I. HISTORY. (Natural Gas). 5 . From Carbon Tetrachloride. 6 . Special Chloroforms of Foreign Manufacture. Chloroform was discovered in 1831, yet i t has been IV. PURIFICATION. asserted t h a t there are indications of a n earlier acv. THE PHYSICAL C O S S T A N T S OF CHLOROFORM: I . Specific quaintance with the compound. For example, we Gravity. 2 . Boiling Point. are told b y Hutman,s on the authority of Johannes VI. THE DECOMPOSITION OF CHLOROFORM: I. T h e Changes Porta3 and Sir Walter Scott,4 t h a t chloroform was which.$Chloroform Undergoes upon Exposure to i l i r . 2. T h e Changes which Anaesthetic Chloroform Undergoes when a Current known in former times and was then employed as a means of producing insensibility. Investigation shows of Oxygen i s Conducted through it. 3 . T h e Decomposition of t h a t this statement is based upon misinterpretation.5 Chloroforna Vapor u p o n Exposure to Gas Light, etc., during Administration. 4. T h e E f e c t of Agitation, upon Anaesthetic See Section VII. 1. of this paper. J . chim. med.. [31 4, 476. Chloroform. 5. The PreserTation of Chloroform. 6. The “Magia Naturalis,” 1619. I t snould be mentioned here that in 1589 Storage of Anaesthetic Chloroform. Giaubattista Porta used an essence made from hyoscyamus, solanum, VII. THE IMPURITIES OF ANAESTHETICCHLOROFORM: POPPY, and belladonna, enclosed in a lead vessel. for producing sleep by inhalation of the vapor. I . Chemical Considerations. 2 . Physiological Considerations. “Letters on Demonology and Witchcraft,” 1830. VIII. THE EXAMINATION OF ANAESTHETIC CHLOROFORM: 6 Most ancient authors who pretend to treat of the wonders of “Natural I . The Tests for Odor. 2. Residue. 3 ( a ) . T h e Test with S u l Magic.” give recipes for calling UP phantoms by the inhalation of certain phuric Acid. 3(b). The Test with Formalin-Sulfihuric Acid. gases from burning medicated mixtures, generally of oils, and by the use 3(c). Discussion of 3 ( a ) and 3 ( b ) . 4. T h e Detection of Water of suffumigations of strong herbs (Hibbert’s “Apparitions,” p. 120). The ancient Egyptians, Assyrians, and Chinese were familiar with many vegein Chloroform. 5. T h e Detection a?zd Estimation of Alcohol Read at the regular June meeting of the New York Section of the American Chemical Society. 191 1 .
table substances (e. g., cannabzr indica) capable of producing ecstatic, sedative and anodyne effects (Snow’s “Chloroform and Other Anaesthetics,” 1858; Bernard’s “Lecons sur les Anesthesiques et sur l’hsphyxic” 1875:
