Feb., 1914
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 C H E M I S T R Y
samples a n d consequently having t o multiply t h e amount of alkali used b y 1.63, i t is advisable t o use a 16.3 cc. pipette, i n which case, t h e reading on t h e burette denotes directly t h e percentage of casein. A very convenient a n d simple form of acidimeter has been lately p u t on t h e market b y t h e author which m a y be used for both t h e “acid test” a n d t h e “casein test.” A series of comparative tests, using both t h e new method a n d t h e centrifugal method, has been carried on at t h e Eastern Dairy School, Kingston. The tests were made independently on t h e same milks b y Messrs. Echlin a n d Cameron. N r . Echlin did t h e work with t h e new test, a n d 11r. Cameron t h a t with the centrifugal method. T h e resulting figures, as can be seen from t h e following table, are in surprisingly close agreement. Centrifugal method 2.6 2.7 2.5 2.55 2.55 2 i5 2.3 2.3 2.6 2.5 2.5 2.25 2.25 2.2 2.5 2.6 2.7 2.3 2.3 2.5 2.45 2.56 2.56 2.55 2.55 2.55
New method 2.64 2.69 2.44 2.61 2.61 3.61 2.36 2.36 2.61 2.53 2.53 2.28 2.28 2.20 2.56 2.63 2.67 2.43 2.43 2.43 2.35 2.67 2.67 2.59 2.59 2.59
Centrifugal method 2.25 2.3 2.35 2.6 2.5 2.5 2.25 2.25 2.2 2.35 2.35 2.35 2 4 2.4 2.35 2 35 2.35 2.3 2.3 2.4 2.4 2.4 ’
j 3 2.25.
New method 2.35 2.35 2.43 2 59 2.51 2.51 2.27 2.27 2.19 2.35 2.35 2.35 2.43 2.43 2.35 2.35 2.35 2.27 2.27 2.43 2.43 2.43 2.27 2.27
Centrifugal method 2.2 2.4 2.4 2.4 2.5 2.45 2.4 2.4 2.45 2.5 2.3 2 35 2.4
Thr average difference for the above sixty-three 0.03+. GORDOKHALL OF CHEMISTRY SCHOOL OF MINING,KINGSTOX. ONTARIO
.. .. ..
..
..
..
.. .. .. .. .. ..
New method 2.27 2.43 2.43 2 43 2.59 2.51 2.43 2.43 2.49 2.55 2.27 2.35 2.43
..
..
..
.. .. .. .. *.
.. ..
.. .. ..
determinations is
I. A NEW ELECTRICALLY CONTROLLED AND TIMED ASPHALT PENETROMETER 11. THE EFFECT ON PENETRATIONS OF VARIATIONS IN STANDARD NEEDLES B y HBRMAXNW. MAHR
Received July 14, 1913
I Success in t h e laying of asphalt pavements is probably more dependent on t h e proper consistency of t h e asphalt cement used t o bind t h e mineral aggregate t h a n on a n y other feature. The varied origins of modern bituminous cements have made t h e determination of their consistency t h e most important test applied t o these materials. Formerly a few varieties of standard solid biteurnens, quite uniform in character, fluxed with definite proportions o€ petroleum residuums of standard and specified composition, yielding cements of a desired consistency, formed t h e bulk of t h e asphaltic cements; b u t recently many paving bitumens obtained b y distilling asphaltic
I33
petroleums t o t h e consistency of cements have come on t h e market. Proximate chemical analysis is of little value in fixing. their origin, a n d t h e highway chemist is obliged t o rely almost solely on determinations of consistency t o ascertain their suitability. There are several rough methods for determining t h e consistency of asphaltic cements, but t h e most generally used scientific determination is b y means of penetrometers. T h e first of these instruments was devised b y Bowen, a n d has been followed b y machines working on t h e same principle by Kenyon, Dow a n d t h e New York Testing Laboratory. The two latter are those generally used a t present. The penetrometer has made i t possible t o control t h e consistency or as usually expressed, t h e penetration, within narrow limits. The penetrometers consist essentially of a needle of specified size (Roberts, KO. 2 ) fixed in a rod, t h e rod and needle being of, or loaded t o , definite weights. A clamp of some nature holds t h e rod with t h e needle, allowing t h e latter to penetrate as nearly as possible without friction. A device for measuring the amount t h e needle has penetrated after i t has been released for a specified time a n d again grasped b y t h e clutch, is also necessary. The penetration is expressed in hundredths of a centimeter. Penetrations are most commonly made a t 2 5 ’ C. ( 7 7 ’ F.) with the needle loaded t o I O O grams penetrating for five seconds. I n order t o ascertain t h e extent a n asphaltic cement will harden when chilled t o o o C. (3 2 ’ F.),penetrations are frequently made a t this temperature with the needle loaded t o zoo grams penetrating for one minute. Occasionally i t is specified t h a t cements shall not show more t h a n a stated penetration a t 37.7’ C. (100’F). or 46’ C. (115’ F.), the needle being under a weight of 50 grams and released for five seconds. The Dow penetrometer frame consists of a base t o which is fastened a broad upright support with two shelves a t different distances from t h e base. T h e needle is held in a n aluminum rod weighted b y a rectangular frame of the same metal. T h e latter is fixed t o t h e rod a t about one-third t h e distance from its lower end. Weights are placed on t h e lower part of t h e frame t o load t h e needle. The above-mentioned framework encloses t h e lower shelf on which is placed t h e sample. The rod passes through a hole in t h e upper shelf a n d is here grasped b y t h e clamp which is closed on t h e rod b y a spring when not penetrating. The rod and needle are released from t h e clamp b y pressing t h e spring together with a button-ended rod. The device for measuring t h e amount penetrated is fixed above t h e end of t h e rod. This consists of a rack, set vertically, t h e end of which can be brought down t o meet t h e t o p of t h e rod. This rack is i n gear with a pinion on a horizontal shaft. T h e latter passes through a graduated dial a n d a n adjustable hand is fastened t o i t there. A counterweight which hangs from a cord winding u p on a small pulley on the pinion shaft allows t h e rack t o be raised or lowered. The divisions on t h e dial correspond t o a movement of I/IOO cm. b y t h e rack.
T H E JOURNAL OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY
I34
T h e Dow instrument has many features which make its use time-consuming. It also requires considerable skill a n d attention t o obtain reqults checking within three or four degrees. T h e shelf, on which rests the water b a t h containing t h e sample, is fixed in position. This limits the height of t h e sample container a n d t h e bath. T h e weighted frame limits t h e width of t h e vessel used for a water bath, a n d is a n inconvenience in placing t h e sample on the shelf a n d setting the needle. When t h e clamp is opened t h e space within is quite large. This allows t h e rod to deviate from a vertical position while penetrating. The weight of the large frame also tends t o bring t h e needle out of t h e vertical. T o avoid this action requires extreme care in setting, a n d even then i t takes place t o a small extent. When t h e rod is again clasped by t h e clamp, it is moved horizontally, t h u s bringing a force on t h e needle other t h a n its weight. On bringing the rack down on t h e rod, after t h e needle has been set or penetrated, its weight is liable t o drive the rod a n d needle down into t h e asphalt. T h e operator is inclined t o avoid this b y stopping t h e rack just above t h e t o p of t h e rod, thus introducing inaccuracies in t h e determination. T h e counterweight a n d its cord often become tangled in the shaft a n d shelves a n d are in t h e way. These objectionable features of the Dow penetrometer led t h e New York Testing Laboratory t o modify it. This instrument is described by Clifford Richardson in his work o n asphalt paving.’ The fixed shelf of t h e Dow machine is replaced by one on a screw. This allows t h e sample to be brought up to the needle very slowly, a n d t h e setting can be made with greater accuracy. The weighted frame is dispensed with and replaced b y a weight on t h e lower part of the rod just above t h e needle. T h e rod slides in a collar of considerable height a n d is t h u s maintained in a vertical position. The clamp holding the rod is fixed in this collar a n d grasps i t more firmly t h a n t h a t of the Dow penetrometer. Instead of a counterweight, t h e rack is kept in position b y a spring pressing against it. T h e wide collar, forming part of t h e clamp of t h e New York Testing Laboratory instrument, gives rise t o considerable friction on the rod. This violates the basic requirement of t h e ideal penetrometer. The clamp requires the exertion of considerable force t o release t h e rod. This tends t o cause t h e operator t o allow t h e clamp t o s h u t before t h e expiration of t h e standard penetrating period. The force required t o open t h e clasp is also,liable t o disturb t h e setting of t h e instrument a n d thus ihtroduce inaccuracies. T h e errors due t o t h e construction of the present machines a n d t o t h e personal equation of the operator often require a long series of determinations in order t o obtain three results which lie within a limit of three or four degrees. Some specifications for asphaltic cement require its consistency t o lie within limits ten degrees apart on t h e penetrometer. It is therefore difficult t o interpret t h e specifications strictly with the results obtained o n t h e present penetrometers. This has given rise t o a demand for a n instrument which eliminates some of t h e constructional errors of t h e present ones, a n d also some of t h e personal errors. I “The
Modern Asphalt Pavement,” John Wiley & Sons
Vol. 6 , NO.
2
T h e errors in penetrating, apart from those of t h e instrument, are quite numerous. T h e sample, usually contained in a small tin box, must be firmly set in the water bath. This can be very satisfactorily accomplished by means of a glass vessel with a deep layer of fairly hard asphaltic cement.l The sample must have been a t t h e standard temperature long enough t o have attained it throughout. I n this connection, laboratories working with a large number of asphaltic cements m-ill find a good thermostat a great convenience. After a sample has been maintained thirty minutes a t cons t a n t temperature it can be placed in the penetrometer water bath, filled with water from the thermostat a t t h e same time. A personal error of considerable magnitude has already been indicated, t h a t of setting the rack on t h e rod before and after penetrating. I n t h e timing of t h e penetration period lies probably the greatest error of the determination. The timing is done by either a stop-watch or a metronome. The use of t h e former is more open t o inaccuracies t h a n t h e latter. T h e variation in the size of t h e standard needles has often beeii pointed out as a source of variation in results obtained by different chemists or by t h e same operator from time t o time. The personal errors have been so large t h a t no definite conclusions could be drawn as t o t h e extent of this source of difference. The importance of eliminating t h e time error a n d shock, due t o the manual control of penetrometers, has long been recognized. With this object in view, Dow a n d Griffith devised a n d patented2 a n electrical limiting-time-interval clamp, t o be applied to t h e then generally used Bowen penetrometer. This clamp clasped t h e thread supporting the weighted bar which held the needle, and released it for the desired intervals. This electrical limiting-time-interval clamp was cumbersome a n d complicated in its working a n d regulation. When Dow devised the penetrometer which bears his name, a n d which superseded the Bowen instrument, he omitted from i t his time-interval clamp. The advent of the simple, compact, Sieman’s intermediate relay with time limits has made it possible t o electrically time a n d control penetrometers of the present type. The penetrating device of the instrument can be directly controlled by the electrically timed magnet, instead of through t h e intermediary of a clamp, as in t h e Bowen-Dow-Griffiths electrical penetrometer. This simplifies the operating mechanism a n d reduces the chances of trouble from its derangement. A new form of penetrometer, electrically controlled a n d timed, used for over a year in this Laboratory, is shown in Figure I . Figure 2 is a sketch of the electromagnetic clutch for holding the rod with its needle. The clutch is on a bracket sliding on t h e upright rod of t h e instrument, t o which i t may be secured by means of a set screw. The weighted rod A, which holds the needle, is of steel, brass-clad. It slides through t h e openings in the thin German silver plates, C C, a n d is partly enclosed b y the concave poles, B, B,, of the electromagnet. T h e plates are set so t h e rod does not come into contact with the poles of t h e magnet, a n d are 1
2
Bull 38, Office of Public Roads, U. S Dept. of Agriculture. U S. Patent 512,687 (1894).
Feb., 1914
T H E JOURATAL OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
rounded where they touch t h e rod, t h u s eliminating all friction. T h e rod a n d needle weigh 50 grams a n d are weighted t o 1 0 0 a n d 2 0 0 grams b y weights of 5 0 a n d I 5 0 grams, respectively, slipped over t h e rod above t h e needle, and there fastened b y set screws. The penetration is measured, as in other machines, b y means of a rack a n d pinion, t h e latter being fastened t o a n adjustable hand on a dial. The counterweight a n d spring, used i n t h e previous types of instruments for holding t h e rack i n place, are dispensed with. T h e pinion shaft has a n additional gear wheel. This gear is in mesh with a worm on a shaft a t right angles t o t h e first, t h e worm shaft being driven b y means of a milled head at one side of t h e dial. B y turning t h e milled head t h e rack may be raised or lowered a n d accurately set on t o p of t h e rod. I n setting t h e needle on t h e surface of t h e sample, t h e latter is first raised t o within less t h a n a millimeter of t h e former. T h e rod is then forced down b y t h e rack until t h e needle touches t h e surface of t h e asphaltic cement. During t h e setting t h e rod is held b y t h e ” m a g n e t ,t h e electromagnetic force being overcome b y t h a t exerted b y t h e
I35
operated b y hand. The circuit is broken b y pressing a button. T o eliminate t h e time errorLof t h e observer, a Sieman’s intermediate relay with time-limit is used. The penetrometer is placed in t h e circuit with one side of this A device, a n d t h e lighting circuit passed through a switch a n d t h e relay electro-magnet. On breaking t h e current through t h e latter, the penetrometer circuit is broken and auto1 I matically made a t the end of 1’ i ’ ,c 1
;
meter was tested by determining t h e penetration of three asphaltic cements, using t h e same needle. The peneFIG.2 trations were made a t 7 7 ” F., with the needle loaded with I O O grams, penetrating for j seconds. After each observation t h e needle was cleaned with chloroform, dried, a n d brought t o 7 7 O F. The results are given i n t h e following table: PENETRATIOK OF ASPHALTIC CEUENTS. ( 7 7 ’ F., 100 g., 5 sec.) Oil asphalt cement No. 1 Determination No. 1.. , , , Determination N o . 2 . . . . Determination No. 3.. . , ,
.
55 55 55
Oil asphalt cement so. 2
Trinidad asphalt cement
53 53 53
85 84 84
I1 Richardson’ has stated t h a t variations in t h e size of t h e qeedles give rise t o uncontrollable.variations i n penetrations determined with them. Since all errors are eliminated in the machine described, i t was possible t o ascertain t h e extent of this variation. Three needles were selected from each of three packages of standard needles. Oil asphalt cement No. I was then penetrated, using these needles, taking t h e precautions outlined above. PENETRATIOU OF OIL ASPHALT CEXEST No. 1, BY DIFFEREX.” NEEDLEY ( i i 0 F . , 100 g , 5 sec ) Seedle
FIG.1
rack. This device and method of procedure enable very accurate settings of the needle a n d rack t o be made. The sample is placed on a movable shelf which can be rapidly lowered t o allow cleaning of t h e needle. I n order t o set t h e machine in a vertical position, a plumb bob a n d adjusting screws are attached t o t h e penetrometer. A small electric lamp, fastened t o t h e top of t h e standard a n d in series with t h e electro-magnet, indicates when t h e current is on. T h e instrument is wound t o be connected t o a I I O volt direct current circuit. The use of t h e electro-magnet clutch precludes t h e shock or displacement of t h e machine, due t o a clamp
Package Penetration Needle
1
1
2
1 1
3 4 5
2 2
55 55 54 54 54
6
7 8 9
Package Penetration
2 3 3 3
55 55 54 54
-
Average, 54.6 T h e greatest deviation from t h e mean is 0.6 of a unit.
c o ~ c ~ u s ~ o ~ ; s . -new - A form of penetrometer, which eliminates t h e errors due t o t h e construction of previous instruments a n d permits rapid accurate determinations, has been described. The personal error in timing penetrations has been eliminated through t h e use of this penetrometer in connection with a n intermediate relay with time-limit. The variations in determinations of penetration due 1
LOC. Cil.
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 C H E M I S T R Y
136
t o variations in t h e standard needles has been investigated a n d found t o be negligible. The writer wishes t o express his appreciation of t h e help rendered by Mr. Walter Erlenkotter a n d Mr. A. D. St. John, of this Laboratory, in connection with this paper. STANDARD TESTINGLABORATORY AND APPORTIONMENT BOARDOF ESTIMATE CITY OF NEW YORE
AN APPARATUS AND METHOD FOR DETERMINING THE HARDNESS OF BUTTERFAT By A. E. PERKINS Received September 22, 1913
T h e desirability of having a n accurate method for determining the hardness or consistency of butterf a t a n d other fats has been felt for a number of years. Several methods a n d apparatus having a greater or less degree of efficiency have been devised from time t o time. T h e first methods were proposed for the examination of olive oil. Of these earlier methods t h e most practical was devised by Serra Carpi.’ His method was t o cool the olive oil down t o 2 0 ’ C., for three hours, a n d b y means of a suitable arrangement, he placed on the solidified f a t a cylindrical iron rod, z mm. in diameter a n d I cm. long a n d conical a t the bottom. Weights were then p u t on t o the rod until i t sank completely into t h e fat. Thus, for pure olive oil 1700 grams a n d for cottonseed oil 2 5 grams were required. Woods a n d ParsonsZ report satisfactory results in determining t h e hardness of butter by the use of a method which consists essentially of dropping a weighted glass rod through a glass tube I meter long, held vertically above t h e surface of the butter t o be tested, a n d noting t h e depth of penetration on a scale attached t o t h e glass tubing. The determinations were performed a t 15.5’ C. after t h e butter had stood in a cool room for several days. The results were expressed in mm. of penetration. R. Brulle3 measured t h e hardness of butter with a n apparatus which he called a n “oleogrammeter.” This is a n instrument consisting of a vertical rod on t h e top of which is fixed a large plate. T h e rod is allowed t o slide in a ring fastened t o a stand. The end of t h e rod is placed on the surface of the solidified fat, a n d then weights are put on the dish until the rod sinks briskly into t h e fat. T h e weights required represent t h e resistance of the butter t o t h e “oleogrammeter.” T h e butter samples were kept a t 2 1 ’ C. for a n hour before testing. This method is essentially the same as t h a t used by Serra Carpi4 for olive oil. Sohns proposes three forms of apparatus a n d lays down the following rules, strict adherence t o which are necessary: I . T h e rod must descend in a n absolutely perpendicular direction. 2
8
‘
Serra Carpi, Z . anal. Chem , 1884, as, 566. W o o d s and Parsons, Bull 13, New Hampshire Exp. Sta R . Brulle, Comfit. r e n d , 1893, 116, 1255. L O C . cit.
I Sohn. Analyst. 1893, p. 218.
Vol. 6 , N0.2
2. I t must slide in its bearing with t h e least possible friction. 3. Conditions of temperature must be constant. 4. l’essels of one diameter must be used for t h e material under examination. 5. The rod must enter t h e center of t h e vessel or a t a fixed distance from t h e circumference. 6. The same depth of material must always be used. 7. T h e material must be allowed t o rest a certain fixed time before testing. J . B. Lindsey’ a n d his associates determined t h e hardness of butter with a n apparatus analogous t o t h a t used b y Woods a n d Parsons,* t h e only real difference being t h a t they dispensed with t h e large glass tube a n d the depth of penetration was measured on t h e plunger. Their determinations were performed on butter which had been in cold storage for some time a n d then allowed to stand a t room temperature for several hours. Hunziger, Mills and Spitzer3 report results in measuring the hardness or ‘ I mechanical firmness’’ of butter with a n apparatus which measured t h e crushing effect of a plunger, size a n d weight not stated, on briquettes of manufactured butter. KO mention is made of t h e conditions of temperature under which t h e tests were conducted. I n some of our experimental work here, we considered i t desirable t o measure t h e hardness of butter f a t with a reasonable degree of accuracy, a n d in such a way t h a t results obtained throughout experiments extending over long periods of time would be entirely comparable. a f t e r trying several of t h e above-mentioned methods, none of which proved delicate enough for our purpose, t h e following apparatus a n d method were devised. The apparatus used, as shown in t h e accompanying cut, comprises a firm support (A) a n d a separate light frame (B) carrying the penetrating needles a n d t h e weights. The support consists of a heavy iron base (c) into which are inserted z upright rods (d a n d e) about I meter long, one of which is hollow a n d contains wires connecting t h e electro-magnet (g) with ( h ) . These uprights are about z j cm. apart a n d are joined together at the t o p b y a piece of hollow iron rod ( J ) : ( h ) a n d ( h ) are binding posts for a t A taching the batteries t o operate t h e magnet. key G) attached t o t h e base serves for making a n d breaking the current through t h e magnet: ( k ) a n d (I) are millimeter scales reading downward. Attached t o the upright rods is a n adjustable platform ( m ) for carrying the sample whose hardness is t o be tested. T h e coarser adjustment of the height of t h e platform is secured by means of t h e clamps (a) a n d ( 0 ) . This adjustment does not need t o be regulated except a t rare intervals. A finer adjustment is secured by simply turning ( m ) which is supported from (n-o) by a ”4 inch n u t a n d screw. The frame is of hollow brass tubing t o get it as light as possible, while still retain1 Lindsey and Associates, 13th A n n . Rept. Hatch EXO. Sta., p . 28; 14th A n n . Rpt. Hatch E x p . Sta., p . 167; 16th A n n . R p t . Hatch E x $ . Sta.. p. 59; Zlst .4nn. R p t . Hatch E x $ . Sta., p. 99. 3 Woods and Parsons, 106. cit. Bull. 169, Purdue University, Indiana Agr. Exp. Sta.
