I S D C S T R I A L A N D ENGINEERING CHEMISTRY
May, 1923
method, they must be treated alike in this respect. The pens are prepared and weighed before being used and are cleaned and weighed after using, as in the other method. The results obtained by the mechanical tester are usually in the same order as those from the closed test, but not in the same ratio. This has been found true especially in dealing with inks in which “negative catalyzers” were added to reduce corrosiveness. One of these substances reduced the corrosion to a very low value when the pen was immersed all the time, but the mechanical tester showed little improvement. An estimation of the amount of “building on the pen,” sometimes confused with corrosion, can be made by observing the appearance of the pen after it has been used in the mechanical tester for a day or longer.
COMPARISON AND RATINQ
Up t o this point nothing has been said about a standard for comparison or a system of rating. Strictly speaking, neither is absolutely necessary. If one ink is to be tested for possible use, a minimum standard can easily be set for i t in each particular. If two or more are to be compared, they can be compared separately in all their qualities and an average made, with due consideration to the particular application of the ink. I n some cases, where a number of inks are to be compared, however, the analyst may wish to have a numerical standard for reference. The system of rating proposed in the earlier government publications is no longer recommended. Indeed, this procedure has been taken more seriously than was intended. It must be emphasized that there can be no hard and fast system of rating which applies to all cases. The author’s suggestion is t h a t corrosiveness, stability,
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permanence, and color be graded 25 each, on a scale of 100. The standards for the separate headings are determined as follows: CoLoR-The initial color and final color are each rated on a scale of 12.5. An entirely satisfactory depth of color, obtained by an ink of known composition, is selected as a standard and graded 12.5. The same ink, diluted to a point where it is entirely unsatisfactory, is rated zero. The intermediate steps are obtained by mixing the two inks in the proper proportions, and the ink under examination is compared with the nearest standard. In the rating of color, especially the initial color, the question of personal preference naturally is a factor. It is suggested that several persons assist in this test, and, if possible, that the user of the ink pass upon the preference as to color. PERMANENCE-The results of the weather test or those of the hypochlorite test may be used. I n either case the inks under examination are compared with a series of inks of known composition, varied by definite ratios of concentration. The ink is then compared with the nearest standard and so rated. The rating may be corrected for the effect of the persistence of the dye, if necessary. CORROSION-High and low limits for loss in weight are chosen arbitrarily, with respect to the reasonable expectations for the ink. A rating of zero corresponds to the higher loss and a rating of 25 to the lower. The rating of the ink is determined by locating the position of the actual loss on this basis. STABILITY-The sediment after a known period of exposure is collected on a filter paper. No sediment is rated 25 and a set maximum is rated 0. The amount estimated by comparison gives the basis for the rating of the ink. For an accurate test, the sediment may be collected in an alundum crucible and weighed. The system of rating must in every case be subordinated to the knowledge of the purpose for which the ink is to be used. In the author’s opinion, however, this system of rating establishes a criterion for the average user.
Apparatus for Dispensing Concentrated Sulfuric Acid and Sodium Hydroxide Solutions’ By Roscoe C. Abbott EXPERIMENT STATION, AGRICULTURAL COLLEGE, LINCOLN,NEB.
The accompanying diagram shows a type of apparatus for dispensing concentrated sulfuric acid and sodium hydroxide solutions for the Kjeldahl nitrogen determination. This apparatus has been used in the feed laboratory a t this station with complete success. ’ Two 500-cc. burets, graduated to 5 cc. with the 25-cc. divisions made prominent, are placed at such a height as to allow the mouth of an 800-cc. Kjeldahl flask to be easily placed beneath them. The beakers beneath are for the purpose of catching any drops of liquid that may drop, and are removed only a t such times as may be necessary for cleaning up. Eight-liter bottles for the acid and alkali are fitted with 3-hole stoppers and placed on a shelf or box a t such a height that the tubes AA‘ extending from the bottom of the bottles may be bent a t convenient angles and reach just to the zero mark of the burets. The tubes DD’ extend through the stopper and are connected to an air line by means of a 3-way stopcock, C. The source of air pressure may be either the laboratory air line or a hand pump; in this laboratory the hand pump has been found very satisfactory. Tubes BB’ extend through the stopper and are bent downward so that the opening may be easily accessible for closing by means of the thumb or finger. A circle of heavy copper wire is placed around the neck of the bottle and the loops extending on either side are twisted together, resulting in small eyelets on opposite sides, to one of which is loosely attached a second piece of heavy copper wire. This wire is placed over the stopper and inserted through the eyelet on the opposite side, drawn tightly, and bent sharply upward. This keeps the stopper from being forced out by the pressure and may be quickly and easily released. T o fill a buret set the stopcock C properly, close the tube B by means of the thumb, and apply the air pressure. As soon as the buret is filled the pump is stopped and the thumb instantly removed from the tube B ; the excess liquid will siphon back into the bottle leaving the buret filled to the zero mark. 1 Received
March 26, 1923.
When a bottle becomes empty it is only necessary to raise it up until the tube AA’ clears the top of the buret; it is set on the table, the wire bent back, and the stopper containing the three tubes is removed as one piece to be inserted in a filled bottle and replaced in position for use.
