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1-9 DEPARTMENT OF COMMERCE Letter

BUREAU OF STANDARDS Circular

WASKTNOT'ON No. 302

(May $5 JV:1931)

Battery Compounds and Solutions

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The Bureau of Standards receives many inquiries about

materials which are said to charge storage batteries or

otherwise improve their performance. More than one hundred of such materials have been brought to the Bureau's

attention during the past few years. A statement entitled

"Solutions do not charge storage batteries" was issued in

the Bureau's Technical News Bulletin No. 9^-, dated February 10, 1925. This statement was based on tests of typical materials available at that time. Since then additional tests on solutions and compounds, the latter in the

form of salts to be added to the battery electrolyte, have

been made. The later tests confirm the Bureau's previous

conclusions that these materials do not charge storage batteries nor do they materially improve the performance of

the batteries.

Careful tests have shown that batteries containing

these solutions behave essentially the same as similar

batteries not containing the materials in question; that

is, no essential improvements in the capacity of the batteries, the time required for charging them, the operating

temperatures, or the amount of water which must be added

to maintain them, have been observed.

It has been shown that batteries are not charged by

changing the solutions and that the time required for

charging is not decreased. The word "charge" as apolied to

the storage batteries ha s a distinct technical meaning. The

American Institute of Electrical Engineers has defined the

word "charge" as follows: "Charge. The conversion of

electrical energy into chemical energy within the cell or

battery. This consists of the restoration of the active

materials by passing a unidirectional current through the

cell or battery in the opposite direction to that of the

discharge. A cell or battery which is said to be 'charged'

is understood to be fully charged." This definition indicates clearly that the charging process is the restoration

of the active materials of the battery by an electric current .

Careful comparison of batteries containing such solutions or compounds with simile r batteries not so treated

have shown that in either case a half-hour charge, the

oattery being discharged initially, will permit the operator to withdraw ampere-hours eoual to about what has been

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put in during the one-half hour charge, and similarly, if the

charge is continued for one hour the equivalent of the onehour charge can be withdrawn. This is in accordance with

fundamental laws of physics and chemistry.

The claim is often made that batteries containing these

solutions will operate at lower temperatures when being

charged by an electric current. The temperature to which the

battery will rise depends uoon the amount of heat energy

which is liberated within the battery and the radiation of

heat from the battery. Assuming two batteries to radiate

heat eaually, the one which has the higher internal resistance will operate at the higher temperature. The electrolyte is only one of several factors in determining this resistance. Careful comparison between batteries containing

these solutions or compounds and similar batteries not so treated have shown that there is very little, if any, difference in the operating temperatures under comparable conditions.

Likewise the claim is often made that the use of such

solutions or compounds will prevent freezing. The freezing

point of a battery electrolyte varies with the specific

gravity. If extra acid has been added so that the battery,

in a state of discharge, has a high specific gravity the

freezing point is correspondingly lower, but this introduces other difficulties.

The claim is sometimes made that these solutions and

compounds make an old battery work like new. Such a statement is rather vague, but one interpretation which might be

placed upon it is the following: If a battery which has

been g iving less than its rated capacity is treated with

such a solution or compound it might be expected t ha t the

full rated capacity of the battery would be restored. Experiments have indicated that this is not the case.

The storage battery ha.s a descriptive name because the

energy of an electric current sipplied to the battery at

one time may be held and used at a later time. The chemical reactions which occur in such a battery are reversible.

During the charging process the chemical r east ions proceed

in one direction, while the delivery of electrical energy

results from the chemical reactions proceeding in the opposite direction. The fundamental reactions in the battery

during discharge result in the formation of lead sulphate at

both the positive and negative plates. When the battery is

being charged, on the other- hand, the lead sulphate is broken

down into constituents of the plates and electrolyte. No

case has been found in which this fundamental reaction is ma-

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terially altered by the use of these battery compounds and

solut ions

.

Since the storage battery stores chemical energy rather

than electricity as such, the question may be asked how far

the chemical reactions may proceed in the battery. Experience shows that, on the average, only 25 to 4-0 per cent of

the active materials in the cell are actually used during

discharge. A battery which has been discharged, therefore,

to a voltage which is below the useful limit can recuperate

to a limited extent if allowed to stand on open circuit for

a short time so that the electrolyte has an opoortunity to

penetrate farther into the pores of the plates and thereby

come into contact with active materials which, have not been

previously converted to lead sulphate. Successive discharges of a battery may be made, therefore, before the battery becomes completely exhausted. Even then much of the

original active material still remains. Changing the solution in the battery may permit some further discharge to be

made as a result of the fresh solution making contact with

active materials already present. This can not, however, be

regarded as evidence that the battery has been charged, because the active materials of the plates have not been restored in any sense of the word.

A battery which is almost completely discharged may

have nearly the same voltage as one which is fully charged.

In this condition the battery may be able to turn the

starter of an automobile or light the lamps, but its exact

state of charge can be determined only by making a measured

discharge upon it, using suitable measuring instruments.

The lead sulphate which is formed on the plates during

the discharge is finely crystallized and quite invisible.

If, however, the battery is allowed to stand in an exhausted

condition for a considerable period of time the crystals of

lead sulphate tend to grow larger and there is also some increase in the amount as a result of local action. In time

the plates may becOcome encrusted with a coarsely crystallized

lead sulphate which is difficult to break down. The condition of the battery at such a time is not due primarily to

the alleged pernicious effects of the sulphuric acid but

rather to failure to charge the battery properly. Lead sulphate is sparingly soluble. Introducing a new solution may

dissolve a small amount of it, but when the solution becomes

saturated with the lead sulphate no more will dissolve.

Analyses of some of the solutions have shown them to

contain about 4o per cent sulphuric acid and some coloring

matter. Other solutions contain about the same amount of
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sulphuric acid and in addition significant amounts of some or

all of the following: sodium, magnesium, potassium, aluminum

and other less common materials. The sodium, for example, mayhave been added as soda, lye, or Glauber's salts, but it seems

probable that the metallic ions mentioned above were introduced into the solution in the form of the common sulphate

salts, such as Glauber's salts, Epsom salts, and alum.

Battery compounds which are not in liauid form have been

found to contain more or less of the materials mentioned

above, with the exception of t he sulphuric acid. Since the

directions for using such compounds ordinarily state that they

are to be added to battery electrolytes or to fresh solutions

of sulphuric acid, the result in the battery is essentially

the same.

The use of sodium sulphate, Glauber's salts, in batteries is an old story. It was suggested more than forty years

ago, but various authorities have stated since that time

that such a material is without beneficial effect in a battery. The Bureau's recent experiments on the determination

of the rate of sulphation of battery plates indicates that

even 4 to 5 P er cent of Epsom salts or Glauber’s salts do

not materially reduce the rate of sulphation.

The indiscriminate addition of these solutions and compounds to a battery is not advisable, although in some cases

no particular harm may be done. If the solution is used to

replace the electrolyte of a completely discharged battery,

as is frequently the case, the battery may be spurred on to

give a little more current because of the surplus of active

material in the plates, but when the battery is recta rged

by an electric current and the lead sulphate in the plates

is reconverted into the active materials of the plates and

has replenished the elect rolyte , the specific gravity will

probably rise much above the limitations for good operation.

In some of the Bureau's experiments it rose to a specific

gravity of 1.365* This is not desirable because the local

action or self-discharge within the battery is materially

increased. A battery containing one of these solutions

lost 47 per cent of its charge in four weeks as compared

with & per cent which was lost by a similar battery with

the ordinary electrolyte. Batteries containing solutions

of higher than normal specific gravity may have considerably less capacity at high rates of discharge, as when

cranking the engine of an automobile, depending on the behavior of the negative plates. The high specific gravity

of the electrolyte is also injurious to the wood separators.

It is a well-recognized orinciple in battery operation that

acid should be added only to replace that which has been spilled,

or in rare instances to adjust the specific gravity to the required standard after the completion of a. full charge.
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