Patented
‘ .
ar. 6, 1923.
CARLETON ELLIS AND VERNON T. STEWART, OF MON'TCLAIR, NEW JERSEY. I
y
I PROCESS OF MAKING ARSENATEFOF LIME;
Application ?led December 19, 1921.
' vNo Drawing.
Serial No.‘ 523,563.> -
To all coho/m it may concern:
a’ manner which yields a product surprisingly
Be it knownthat we, CARLE'roN ELLIS and
VERNON T. STEWART, citizensof the. United
States,‘and residents of Montclair, in the
county of Essex and State of New Jersey,
l'owin water soluble arsenic and which like- ~
have inventedv certainnew and useful Im
localit1es) to. contain at least 40% arsenic
wise apparently conforms to the lega-l'and
commercial requirements for arsenate oflime. -
Arsenate ofllilne is required by law (in some
provements in Processes of Making Arsenate pentoxide ‘substantially- in the combined
of Lime, of which the following is a speci form. ‘ ‘It should not contain in excesslrof
0.75% Water solublev arsenic calculatedias
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?cation.
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1
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This invention 'relates to a process. of the pentoxide. ' The product‘must be volum-ir
makingcalcium arsenate or as it is generally nous powder of such bulk/that one pound
hereinafter termed “arsenate of lime” inas~ will occupy'a; space‘of .from'80,_to_,100“ cubic ; ~
much as it is not pretended that the product inches. ‘ _,The_ commercial requirements ‘are
15
.
islchemically pure, and relates especiallyto that the productshould be relatively‘cheap
a simpli?ed procedure of manufacture which and hence should be capable of manufacture
enables the product to be made in acheap onthe large scale without the employment
and e?icient manner.
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of‘skilled labor in undue amount.
Gener
Heretofore it has been customary to pree ally a product is; desired which is white in
pare arsenate of lime by .the'so-ca-lled wet color in preference .to products which are
20 process involvingprecipitation in highly brownish in color or off color, although the
dilute solutions and consequently involving intrinsic merit of the insecticide is generally
‘operations handling a great‘ bulk of ma not impaired by color variations as these I
teria-l. Aside from the trouble and expense are not usually. based on any chemical al
of carrying out the process in this manner
teration.
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there is theadditio-nal item of depreciation .‘lVe ‘have found it possible to meet these
legal and commercial ‘requirements through
on a plant operating by the wet‘ method.
Arsenate of lime has been found the vmost the dry slaking, process which will be here-v 1
satisfactory insecticide with which to com inafter set forthandwhich in some respects
bat the ravages of the boll weevil inthe cot at least has derivation in our copending ap
ton ?elds.
However in order to produce plication Serial ,431'348, ?led December 17,
arsenate of lime to meet the requirements of ‘
the-cotton grower it is important to have‘
Our investigations have shown that‘ when
an aqueous solution of arsenic acid is added
senate to be prepared cheaply and rapidly in to quick lime which is in a coarse lumpy form
large quantities in order that the seasonal action takes place at the surface‘with the
demand for the insecticide may be readily formation of what appears to be the dical
available a method which will enable the ar
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40
met. Methods looking to the production cium arsenate, while a comparatively small ‘
of arsenate of lime without the employment proportion isv transformed into the desired
of a large bulk of water in precipitation tricalcium arsenategwon the other hand if
have been considered and proposals have‘ the quick lime ;is ground to a ?ne granular
been made for treating ‘lime stone with condition or. even better to a ?ne pulverulent
arsenic acid and also treating a paste of state and arsenic acidsuitably proportioned
sla-ked lime with this acid. So far as we and containing a predetermined amount of
are advised these methods are impracticable water ‘is added thereto, violent reaction takes
45 'for various reasons. The content of soluble place with the formation of a very substan
- arsenic is such that the material could hardly tial and entirely satisfactory‘proportion of
be expected to serve as an insecticide. The tricalcium arsenate. .The more complete
presence ‘of water soluble arsenic in any sub-' conversion to the desired tricalcium com
pound apparently also; is effected by agita
Dry m’ethods'of preparation are. therefore tion and. we preferably employ mechanical
so far as we are advised generally considered ‘agitators in the receptacles employed for
' stantial amount is ruinous to vegetation.
50
carrying outthe reaction.‘ The addition of
In accordance w1th the present invention the ‘arsenic acid solution gradually to " thev
wholly unfeasible.
powdered quick limealso is advantageous
ess'ot' dry slaking quicklimewith arsenic acid because it allows action on the surface of
we have found it possible to carry out a proc-.
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containlng a certain proportion of water' in the particles to take place
the presence oi '
Memes
an excess of lime and as the surface of each would it be likely to spread over vegetation
particle becomes coated with'the arsenate, in the form of a ?ne dust in the same manner
the heat of reaction and agitation serve con
stantly to expose fresh surfaces of the par
as would be'o'btainable by our product when
slaked under preferred conditions. _
ticles and thus advantageously keep the
In fact with high calcium lime in a ?nely
quick lime in excess.’ By this comparatively ground state and arsenic acid of 75%
719
attempting to produce a product of thisde ing body which acts more like a ‘liquid than
scription in a cheap and simple manner. a solid in view of the buoyant effect of the
The lime employed in the present invention steam disengaged during the reaction. is preferably what is known as high calcium
This condition as indicated affords a
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simple procedure we are able to overcome strengththe reaction is so violent that the
- the obstacles heretofore in the path of those mass of quick lime becomes a seething boil
lime- in contradistinction to the dolomitic
or high magnesium limes. While it is pos
bulky voluminous product corresponding
very favorably in legal bulk requirement to
15 sible to use dolomitic or magnesium lime products
made ‘ by the more expensive 80
for the purpose‘ it is generally better to use method of wet precipitation.
lime produced from. the high calcuim lime
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As noted, mechanical agitation preferably
stone. We regard the heat of slaking as should be employed and this preferably
having a distinctly favorable in?uence on should be vigorous in order to constantly
the reaction and by employing the joint bring fresh particles of the quick lime ma
agencies of heat developed by slaking and
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terial into contact with the spray or incom
heat developed by the union of arsenicacid ing stream of arsenic acid solution. Owing
with lime, conditions obtain which lend to to the amount of dust produced in the op
a highly complete conversion to tricalcium eration it is‘ best that the reaction be car
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arsenate.
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ried out’ in a closed vessel or one ?ttedv with 90
The strength of solution of arsenic acid dust collectors. The process may be an in
employed. may be varied somewhat .to meet‘ termittent one, that is a batch process, or it ‘
different requirements in grades of lime and may be carried out in a continuous or non
other conditions-but preferably we employ cumulative manner as for example by feed
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the solution in quite a concentrated form. ing a stream of crushed quick lime along a
For example 75% strength of acid is a conveyor and adding a stream of arsenic
heavy viscous liquid of a speci?c gravity acid solution in the proper combining pro
~
about 1.88. An acid of this strength fur portions.
nishes enough water for the desired degree
After the reaction is ‘completed the prod
of hydration advantageous for opening the uct may be suitably screened or ground if
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lime particles and permitting the ingress desired and preferably is passed through
and reaction of the arsenic acid. Acid of an air separator where by air ?otation any
75%. strength is furthermore .a convenient coarse, gritty particles, silica and other for
form to handle and store.v _While as stated eign substances originally present in _ the
40 the acid of this strength is a suitable one, lime stone or any unburned lime “cores” and 105
it should be understood we do not limit our
the like are removed.
In this connection
selves to acid of precisely this strength ‘but We‘ recommend the quick lime employed be
may use weaker or stronger acid according well burned _in order to as completely as
. to the nature of the qucik lime employed, the possible eliminate cores. Calcium carbonate
45 ‘size of the vessel‘ employed for slaking and (i. g. unburned limestone, etc.) is prone to 1 1'0
other conditions.‘
Thus an acid having a form the mono- or di-calcium a'rsenate and
strength between 50 and 75% maybe em therefore is undesirable except‘ in such small
ployed with limes of high calcium content quantities as must necessarily be present un
and between 75 and 90% with limes of lower der good conditions of operation. On the
50 calcium content in some cases so that we dov other hand we do not wish to- limit our
115
not wish _to lay down any hard and fast rule selves tolime stone which is substantially
with respect to the precise concentration of free from unburnt lime or‘ calcium car- ,
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the arsenic acid, it preferably being of such bonate. The heat ofreaction coupled with
strength that when added gradually to the the agitation is such that even any carbonate
powdered quick lime the formation of moist if present in small amounts may be expected
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or putty-like masses doesinot occur. . This to react to better advantage than when lime
regulation of the slaking and reaction is con stone is being treated with arsenic acid solu
trolled not only by the proportion of water tion under ordinary conditions. While
present but by the rate of addition of the therefore our process permits of the pres
‘arsenic acid solution. It is furthermore de ence of some carbonate with considerable 125
sirable‘ to have the ?nished product in a safety, We nevertheless recommend the em
dry pulverulent condition hence the-addi ployment of a well-burnt quick lime in the
tion of arsenic acid which is.too much di preferred operation.
luted would yield a moist product which
The arsenic acid employed preferably is a
65 could not be '.packaged satisfactorily nor quite ‘free from arsenious oxide ‘as the latter 130
60
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1,447,938
will ‘form products dangerous to‘ vegetation. soluble. arsenicv ‘very, materially-below the
The arsenic acid used may be madeby any
maximum," percentage legally allowed. ‘In
suitable method, as vfor example .by oxida another. case the/same proportions- of 'quick
tion of white arsenic with nitric acid or 'a vlime: and arsenicacid were employed but
process described in our copending-applica the. solution of.‘ the latter was,“ ?rst heated
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tions according to Whicharsenious oxide to boiling. vThe vigor of. the reaction vwas
even more pronounced and the resulting
or arseni‘ous acid is treated with chlorine;
As has already been noted the preferred product showed v.a vcontent of 42.8% arsenic
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form of the invention contemplates the use
of ?nely ground or. crushed quick lime. We
have‘ secured excellent results with quick
lime passing a. sieve of 80' meshes per inch.
No bene?cial results apparently. will be ob
pentoxide and soluble .arsenic as'rpentox
of- ?neness although there is no objection
to such use- On the other hand the lime
may be considerably coarser than 80 mesh
but preferably we make use of particles
notedin the example, there also vmay be
noted, This appears to affect the" calcium
more than the arsenic content, thus theacon
particles of quick lime, the rate of addition
ing no allowance for such losses.
ide 0.3%.‘
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;.The preferred form of product has as
primary components tricalcium‘ arsenate
and calcium hydrate. Steamis evolved‘dur
tained by using lime of any higher degree ing the reaction when using the/ proportions
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some dust loss aswas the, case in the example
crushed to‘ a size ?ner than wheat“ We may tent of arsenic ,pentoxide found by vanalysis
note however at ‘this point that we believe according to the example is slightly. higher ». 8.5
there is a relation between the size of the than the calculated percentages ‘when mak
20
of the arsenic acid andv the degree of agita
tion. If the fragments of quick lime are
quite coarse, asifor example substantially
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, I
The product is preferably air-separated
to remove the coarser particles. ,
‘Y If additions of other substances are re
90
quired these substances may be introduced
agitation is recommended with relatively into the lime orithe acid or into the ?nished
slow addition of the arsenic acid solution product, which’ ever vis more appropriate.
coarser than wheat an especially vigorous
so th-at'an excess of lime is present and , hus, dextrine-to afford better adhesion, cal
time is permitted for the reaction at the cium stearate to make the product somewhat
surfaces of the fragments to progress com less affected by water and other organic or
pletely before they come into contact with mineral substances may be introduced ac
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95
an additional amount of arsenic acid. The cording to any special requirement.
What We claim is:
?ner the particles the greater the surface
of exposure and consequently the less dan
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1. The process of making arsenate of lime
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ger there is of an undue amount of arsenic which comprises gradually adding concen
acid bringing about localized conditions re trated aqueous ‘arsenic acid to powdered
sulting in the formation of soluble‘arsenical quick lime of high calcium content in‘ a
compounds. On the other hand with the state of ”agitation, the proportion of water
540 coarser fragments the area of surface avail present in the arsenic acid being sufficient
able. for reaction is substantially reduced only to yield a pulverulent product.
2. The process of making arsenate of
and this condition should be given consid
lime
which comprises graduallyadding con
eration in carrying out the process where
it is desired to maintain a high standard centrated aqueous arsenic acid to powdered
quick lime in a state of agitation, the pro
e for the product. \Ve recommend therefore portion
of water present in the arsenic acid
that the quick lime be ground so that it will
pass a screen of 8 or 10 mesh‘and upwards.
As an illustration of the method embraced
under the present invention the following
will serve.
.
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110
being only suf?cient to yield a pulverulent
product.
>
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3. The process of making arsenate of lime’
which comprises gradually adding concen
115
5 parts by' weight of quick‘ lime practi trated aqueous arsenic acid to powdered
cally free from magnesium compounds and quick lime of high calcium content in a
ground to 80 mesh were placed in a recep
state of agitation the proportion of water
tacle and approximately 6 parts by weight present in the arsenic acid beingonly suf?
of arsenic acid of 75% strength was slowly cient to yield a pulverulent product and the
added to the pulverized quick lime while the proportion of arsenic acid being suflicient
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120
to form an arsenate containing at least 40%
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tion was violent. The product was'allowed of combined arsenic pentoxide.
LL. The process of making arsenate of lime
to cool and was found to be aIWhite bulky
,material was constantly stirred. The reac
60 powder.
The content of arsenic pentoxide which comprises mechanically. agitating a 125
was found by analysis to be 42%.
The body of ?nely crushed high calcium quick‘
amount of Water soluble arsenic as arsenic lime and gradually1 adding thereto a solution
- pentoxide was 0.22%. Thus theproduct had of arsenic acid containing waterto render
in excess of the 40% arsenic pentoxide re it of \approximately 75 per cent strength
65
quired by law and also had a content of thereby furnishing water to expand and re-.
1 30
menace
‘act with the quick lime, permitting the agi arsenic acid solution whereby substantially”
tation to continue during the addition of complete combination of the latter with the
the arsenic acid solution whereby substan lime occurs to form arsenate of lime con
tially complete combination of the latter, taining less than 0.75% of Water-soluble ar
with the'lime to form arsenate of lime‘ sub‘ senical compounds and at least 40% of com
stantially free from water-soluble arsenical
bined arsenic pentoxide.
I
which comprises mechanically agitating a
body of ?nely crushed high-calcium quick
lime and gradually adding thereto a solution
of arsenic acid containing Water to render
it of approximately 75 per cent‘ strength
thereby furnishing Water to expand and
concentrated solution'of arsenic acid con
taining water' to an excess of pulverized
7. The process for the manufacture of cal
compounds occurs.
5. The process of making arsenate of lime cium arsenatev which comprises adding a
10
M1)
quick lime with agitation and regulating the
addition of the acid solution to maintain
the mass largely in a non-pasty pulveru
lent condition during the reaction.
8. A process which comprises slowly add 45
.15
I agitation to continue during the addition of ing concentrated arsenic acid solution to
the arsenic acid solution whereby! substan ?nely ground quick lime, while thoroughly
tially complete combination of the latter agitating the mass, the proportion of water
with the lime to form arsenate of lime sub being such as to yield a pulverulent product.
9. A process which comprises slowl vadd 50
20 stantially free from water-soluble arsenical
compounds occurs and containing at least ing concentrated arsenic acid solution to .
react with the quick lime, permitting the
40% of combined pentoxide.
finely ground quick lime, While thoroughly
_ 6. The process of making arsenate of lime agitating the mass, the proportion of water
which comprises mechanically agitating a being such as to ield a pulverulent prod
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body of ?nely crushed high calcium quick not, the rate of a dition of the arsenic acid
lime and gradually adding thereto a con solution being sov adjusted as to avoid the
centrated aqueous solution of arsenic acid formation of a mass of putty-like consist
thereby furnishing water to expand and re ency at any sta e of the rocess.
ARLET N ELLIS.
act with the nick lime, permitting the agi
VERNON 'll‘. STEWART.
tation to continue during the addition of the
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