US1842908A - Flaked lead acetate - Google Patents

Description

Patented Jan. 26, 1932 UNITED STATESOPATENT OFFICE RALPH IE. LAWRENCE, OF WICKLIFFE, OHIO, ASSIGNOR TO THE GRASSELLI CHEMICAL" COMPANY, OF CLEVELAND, OHIO, A CORPORATION OF DELAWARE FLAKED LEAD ACETATE No Drawing.

This invention relates to lead acetate in the form of thin flakes.

Neutral lead acetate crystallizes with 3 mols of water of crystallization. It is commonly made by concentrating a clear solution of lead acetate to a high gravity, say 85 B., and then running the heavy syrup into pans. It forms under these circumstances super-cooled masses which remain for some time in the fluid state and then solidify as a whole to hard and compact, large size agglomerates. The further handling of this product involves much manual labor in the removal from the pans, breaking up of the blocks and'packing which creates a serious occupational health hazard.

I have now found a process whereby lead acetate can be produced in a physical form in which it is easy to handle, obviating the necessity of breaking it up or disintegrating it and doing away with much manual labor and its inherent disadvantages. The so produced lead acetate appears in the form of thin, compact, co-herent flakes in which physical form I am not aware that lead acetate has ever heretofore been produced, though it has in this form considerable practical advanof solidification that the product would break up on removal into an irregular powder with much dusting, which would create either a serious health hazard or necessitate exten sive dust collecting equipment.

I have found that by inducing the crystallization of concentrated lead acetate liquor films solidification takes place gradually, passing through a stage where the lead ace- Applieation filed October 14, 1929. Serial No. 399,710.

tate has a waxy consistency. The film can atthis stage easily be scraped off, whereby it breaks up into small, co-herent shavings like flakes, which do not dust, and solidify finally into hard and compact individual flakes.

A technically very convenient manner of inducing the solidification of a syrupy lead acetate film is to bring it into contact with solid lead acetate'and I found that this is particularly easily achieved by first coating a cooling surface with a thin layer of solid lead. acetate; the syrupy melt of additional lead acetate applied thereto solidifies gradually passing through a waxy state of con sistency. 'A thin film of waxy lead acetate is so formed. It does not, while in this state adhere very firmly to the base layer of solid acetate; when scraped ,ofi from said solid layer it separates into non-dusting, nonsticky soft flakes, or shavings,'which soon solidify into hard, coherent flakes of more or less regular shape, usually about one millimeter thick, several millimeters long and a :few millimeters wide.

The product in this flake form weighs, when packed, from to TOlbs; per cubic foot packing space; the flakes are easily soluble and conveniently handled by the consumer.

The flaking of lead acetate according to my novel process is conveniently achieved on so called drum soli-difiers or drum coolers. This type of apparatus consists in its essential )illtS of a feedin device such as a trou h or feeding channel containing the liquid to be solidified, of a rotating cylinder which is in contact with the liquid in the feeder and on rotation picks up some of the liquid which adheres to its surface and solidifies thereon in contact with the atmosphere and of a scrap ing device which removes the solidified material from the surface of the drum. Provision is usually made to cool the inside of the drum with a gaseous or liquid cooling fluid. .In preparing my novel flaked product I used a solution of lead acetate of 1%. at 100 C. Some of this liquor was poured upon the surface of a rotating cooling drum and rub-bed over the surface of the drum by means of a brush forming uniform layer thereon which crystallized and adhered to the drum.

2. Lead acetate in the form of hard, com- The knife edge of the scraper arrangement pact and co-herent flakes which weigh, when was then so adjusted as to leave a thin coat packed from about 50 to 70 lbs. per cubic of this original, solid lead acetate on the foot.

drum.

A very convenientmanner of feeding the concentrated lead acetate liquor upon the drum cooler coated as described above with a thin layer of solid lead acetate was found to consist in running a stream oft-the liquor down an incline which ends in a piece of sheet steel fitted closely to the layer of solid acetate, at the back, underside of the drum, tangent to the surface and parallelto the axis of the drum. The acetate liquor accumulates in the channel formed between the steel sheet and the drum and is from there picked up during revolution forming a liquid film upon the original base layer of solid acetate and solidifies uniformly thereon.

The 85 B. acetate liquor when fed in this manner to the druinstarted to solidify after a few seconds in contact with the solid acetate, which serves as a seeder. The speed of revolution of the drum and the cooling were adjusted to give the lead acetate film about 23seconds time between its formation at the feeder and its removal by the scraper. It had during this time solidified to a waxy, nonsticky consistency and it broke oil atthe knife in the form of soft, non-sticking flakes which in a few minutes after leaving the scraper setto compact, hard flakes. The packed weight of the product from this particular run was 67 lbs. per cubic foot; it analyzed 55.8% Pb, whereas the theory for Pb (0 1 1 0 3H O is 541670. indicating a slight drying action during the process, which, however, is not objectionable. The packed weight of the product made by my process varies generally between the limits of about 50 and 7 0 lbs. per cubic foot. The color of the product depends upon the purity of the liquor used, and when this is of good quality a snow white flaked lead acetate is obtained.

The performance of my novel process can be varied in various ways without departing from the spirit of my invention provided the solidification of the lead acetate liquor is so conducted that it takes place gradually through a stage where it has a waxy, nonsticky consistency. at which stage the acetate is separated into flakes.

It is further understood that the term lead acetate used herein with its usual commercial meaning of neutral lead acetate containing in the neighborhood of 3 mols of water of crystallization.

The process of producing flakes of lead acetate as disclosed herein is claimed in my divisional application Serial #513,784, filed February 5, 1931.

I claim:

1. Lead acetate in the form of hard, coinpact and coherent flakes.

In testimony whereof, I aflix my signature.

RALPH LAlVRENCE.