0
64MM
Pipet Washer
0.R
r-
?-
JOHN H. JORDAN, JR. Technical Department Refining Division, Magnolia Petroleum do., Beaumont, Texas
a-
SIMPLE device for washing pipets rapidly with minimum
A expenditure of labor is shown in Figure 1.. A dozen or more pipets can be cleaned in about 5 minutes with practically no attention from the operator. The apparatus consists of a pipet washer, a pipet holder, and a vessel, such as a 1000-ml. graduated cylinder which can be filled with cleaning solution to a depth sufficient to immerse the pipets completely. The washer is a siphoning device constructed from glass tubing and mounted in a vertical position on a ring stand or similar appliance. It fills and empties automatically on the principle of the Soxhlet extractor. Water enters the washer through the bottom inlet tube and fills the washer to the level a t which the siphon begins to operate, rapidly emptying the vessel. The size of the siphon tube and the rate of water flow to the washer are adjusted so as to complete the cycle of filling and emptying in about 45 seconds. A screen wire is placed in the bottom of the washer for supporting the holder. The holder facilitates the transfer of the pipets from the cleaning medium to the washer. I t is constructed from stainless steel welding rods, although glass rod may be used. Three rings made of the same materials and slightly smaller in diameter than the washer are welded to the rod in the position shown. A few short rods are welded across the lower ring to serve as a screen to support the pipets. Pipets to be cleaned are placed in the holder in an inverted position, to allow rapid filling and draining, and immersed in cleaning solution in the cylindrical vessel. After the pipets are filled with the solution, the holder is raised and pipets are allowed to drain before being placed in the washer where they are rinsed with water. This procedure may be repeated several times if necessary.
Sulfamic A c i d as an
Aid
56 MU. 0 R
i' $
1,
P Figure 1.
Washer and Pipet Holder
Sizes of equipment shown are sufficient for accommodating eighteen 1- to 2-ml., twelve 5-ml., or eight 10-ml. pipets, but these sizes may be altered depending on local needs. The same principle may be employed for washing large pipets or burets, provided the dimensions of the equipment are properly adjusted.
in the Analytical Electrodeposition of Copper
LOUIS SILVERMAN, 5559 Hobart St., Pittsburgh, Pa.
T
H E employment of sulfamic acid in the analytical electrodeposition of copper has not been described. Nitrous acid, which retards the electrolytic deposition of copper, is rapidly decomposed by sulfamic acid, with the formation of nitrogen: HOSOzNH2
+ HONO
-+
(H0)zSOz
+ Nz + H2O
When copper is electrolytically plated from a nitric acid solution, urea is usually added to remove the nitrogen oxides that are formed. Air stirring, if available, accelerates the deposition, but does not remove all the nitrogen oxides. Objections to urea are:
A dark coating may form over the cathode. The subsequent precipitation of nickel by dimethylglyoxime may be incomplete. The removal of 'nitrogen oxides by urea is slow, often unsatisfactory. The acidity of the electrolyte is decreased, and additional acid must be pipetted into the electrolyte.
Table I.
Electrodeposition of Copper and Lead in Bronze (Alloy, 1 gram of 0.07% lead, 70% copper) Deposition" Time of Treatment
Amperage
+
1 2 3
1 75 1.75 1.75
Air stirring sulfamic acid b Only air stirring Previous boiling of one hour, no stirring
4 5 6
1.75 1.75 1.25
Urea, no stirring Starch no stirringC Sulfa& acid, no stirring6
Minutes 45 60 105
,
3 2 1.75
a Each figure is for a set of four samples of same composition, and is complete deposition time for copper and lead. b 0.5 gram of sulfamic acid, maximum. Starch, added a t start, forms a dark coating over cathode.
dissolved in nitric acid and water, boiled for 15 minutes, cooled, then placed on the electrolytic board. The copper did not deposit. Electrolytes treated with urea did not plate, but those to which sulfamic acid (1 gram) was added plated within a few minutes. In Table I, some observed values of time of depositions are given. All experimental work refers to electrolytes containing lead, copper, nickel, zinc, and nitric and sulfuric acids. Completeness of deposition was determined by raising the water level
These statements do not apply to sulfamic acid. There is no organic material present; the nickel determination is not affected; the nitrous acid reaction ( 2 ) is rapid; and the acidity of the solution is unchanged. Furthermore, if an occasional electrolyte is found that will not deposit copper, sulfamic acid will be of assistance. This has occurred in the determination of small amounts of copper in aluminum-zinc alloys. The alloys were
270
