Department of Pediatrics, Yale University School of Medicine, and the Grace-New Haven Community Hoital
PRESENT ADDRESS: Children’s Hospital, 1740 Bainbnidge Street, Philadelphia, Pennsylvania.
PEDIATRICs, November 1959 814
T
lIE THERAPY of infants with disturbancesin fluid balance is greatly assisted by
knowledge of the specific gravity of the
urine. Frequently only a few milliliters can
be collected at any one time, while a
mini-mum sample of 25 ml is necessary for use of the smallest uninometers currently
avail-able. The existing methodsl_4 of
determin-ing specific gravity of one drop of urine
are somewhat laborious, and require
expen-sive equipment and the services of a
rela-tively skilled technician.
The present report describes a method
which is rapid and simple and requires only
a few drops of urine in its use. It is similar
in principle to the determination of specific
gravity of blood by the copper-sulfate
method. For use with urine, mixtures are
employed of two relatively nonvolatile
liq-uids, immiscible with water, and with
spe-cific gravities nearly equally above and
below the range in urine. The specific
gravity of urine is determined by allowing
one drop to fall into each of a series of
tubes containing a mixture of the two
liq-quids made up to various specific gravities
ranging from 1.005 to 1.030 (Fig. 1). That mixture in which the drop of urine comes
most nearly to remaining still (neither rising
nor falling after coming to rest)
approxi-mates the specific gravity of the urine. The
total sample needed is only a few drops,
which can be quite small if a dropper with
a small opening (2 mm) is used. The
deter-mination takes a few minutes. A year’s
sup-ply of the mixtures can be made in one
aft-ernoon and costs less than $6.00.
MATERIALS
The two solutions used were selected from
the flotation method of Kirk,4 using a density
gradient system. These are Liquid 1, dibutyl-n-phthalate (Eastman), specific gravity 1.048200;
and Liquid 2, kerosene, specific gravity 0.8220#{176}.
(Similar results were obtained by substituting
California mineral oil, specific gravity
0.842-0.88420#{176}, for kerosene.)
Mixtures with specific gravities from 1.000
to 1.030 in 0.005-unit increments were
pre-pared according to the following equation:
Weight of Liquid 1 + Weight of Liquid 2 =
Weight of Mixture.
Therefore:
(Density1) (Volume1) + (Density2) (Volume2) =
(
ty1 xt.) I xt.)A sample calculation is given in the
Appen-dix and a representative set of volumes and
weights for a specified amount of stock
solu-tion at the standard reference temperature of
20#{176}Cis shown in Table III in the Appendix.
For calculations at other temperatures the
fol-lowing procedure is recommended.
The densities of the Liquids 1 and 2 are
determined by weighing an accurately
meas-ured volume of liquid at room temperature in
an analytical balance. Then using the above
equation, the approximate weights of Liquids
1 and 2 to be mixed for the desired specific
gravities of the mixtures are calculated.
Ap-propriate amounts of the liquids are then
weighed out and mixed. The specific gravity
of each of the resulting mixtures is then
deter-mined by accurately measuring each of their
densities and converting this value to specific
gravity by dividing by the density of an equal
ITM__#{149}_
-Fic. 1. Apparatus.
COMPARISON OF CALCULATED WITh MEASURED
SPEciFIc GRAVITIES AT 28.5#{176}C
Calculated Measured
1).9!)’ 0.994
I .001 1 .00’2
1.006 1.007
1.011 1.013
1(116 1.018
1.0’21 1.03 1.0t) 1.08
I.084
1.035
SPECIAL ARTICLES 815
The actual values for specific gravities may
differ from the intended values by 0.002, but
this fact does not alter the usefulness of the
mixtures. However, if exact intervals are de-sired, the amounts of either Liquid 1 or 2 to be added to correct the mixture can be calcu-lated by substituting the mixture for Liquid 1 in the equation. Kerosene is used to make the
new mixture lighter and dibutyl-n-phthalate to make it heavier.
RESU LTS
Table I shows the close agreement at
TABLE I
28.5#{176}Cbetween the theoretic specific
gray-ities obtained by calculation from the
for-mula using the measured specific gravities
of Liquids 1 and 2 and those obtained by
direct measurement of the resulting
mix-tures. While these results might provide
adequate justification for use only of the
above formula in the preparation of the
mixtures, confirmation of the predicted
value by direct measurement is desirable.
Variation of Specific Gravities of the Mixtures with Temperature
Figure 2 shows the variation of the
spe-cific gravities of the mixtures measured
over a range of temperatures likely to be
encountered in most clinical situations
where the test might be used (22 to 29#{176}C).
The maximum discrepancy from the
inter-mediate temperature of 25#{176}is approximately
±0.0025. This variation is less than the
specific gravity interval of the mixtures. It
is small because the density of both the
mix-tures and that of water (urine) tends to
change only slightly with temperature. The
.-___
_
1.020-
1.010-
1.000-22
TEMPERATURE (#{176}C.)
FIG. 2. Variation of specific gravities of various mixtures with temperature. -.
%.,_
I .03
0-
I->
0
C-)
U-C., LU
Cl)
I I
25 29
is l)ut half of that of the mixtures. Accord-ingly, for practical purposes no correction for temperature need be applied. For more accurate determinations, interpolation from the curves of Figure 2 may be made, or ideally tile test can be done in a constant
temperature room.
Stability and Useful Life of the Mixtures
Test tubes of 10-ml capacity were filled
with tile various mixtures and used
repeat-edly for varying lengths of time without
renewing the mixtures or removing any of
SPECIAL ARTICLES 817
TABLE II
CHANGE IN SPECIFIC GRAVITIES OF MIXTURES AFFER
I MONTH OF HEAVY USAGE AT C
1-month Sample Stock Sample
1.002 1.007
1.012 1.011 1.013 1.017
1.04 1.03
1.0’25 1.028
1.037 1.033
become slightly cloudy. This tendency was
found to be a function of the kerosene rather
than of the dibutyl-n-phthalate. Substituting
mineral oil for kerosene did not affect the
method, but did not prevent this tendency.
The cloudiness could be removed by
pass-ing the mixture through filter paper
(What-man No. 42). The stock solutions appear to
be indefinitely stable, although kerosene
tends to turn yellow after 8 to 10 months
standing; there is no appreciable change in
specific gravity.
Table II shows the change in specific
gravity of mixtures after 1 month of heavy
usage without replacement of the mixture
or removal of the urine. The general
tend-ency is for the specific gravity of the
mix-ture to become lower. However, even in these most unfavorable circumstances, the
most extreme variation was only 0.005. In
view of this tendency it is recommended
that the mixtures be used for only 2 weeks
before replacement. Ideally the urine
should be removed from the tubes with a
dropper at frequent intervals for two
rea-sons: first, this will help prevent cloudiness;
and second, it will allow the drop of urine
to fall through the surface of the mixture.
If there is a layer of urine on top of the
surface of the mixture, the falling drop of
urine will mix with the layer of urine and not
enter the mixture. Introducing the drop of
urine with the dropper below the surface of
the mixture is not recommended, as in this
case a much larger drop must be used before
it will leave the dropper. It is also easier to
impart a false direction to the movement of
the drop as the dropper is withdrawn.
General Formula:
Appendix: Sample Calculation
(Specific Gravity) (Volume) + (Specific Gravity) (Volume) = (Specific Gravity) (Volume)
Liquid 1 Liquid 2 Mixture
For 600 ml of mixture at specific gravity 1.005 at 20#{176}C:
dibutyl-n-phthalate kerosene
(1.048 gm/mI) (x) + (0.82 gm/mI) (y) = (1.005 gm/mi) (600 ml)
x + y = 600 ml
Therefore: 1.048x + (0.82) (600-x) = 603 gm
1.048x + 492 gm - 0.82x = 603 gm
0.228x :: 111
x = 486.85 ml dibutl-n-phthalate
y = 600 - 486.85 = 113.15 ml kerosene
Therefore: (486.85) (1.048) = 510.21 gm dibutyl-n-phthalate
(113.15) (0.82) = 92.79 gm kerosene
Specific
(;rat’ity
Acknowledgment
The author wishes to thank Dr. Ira K.
KoNsw ULICH, M.D.
Volume Weight Volume Weight
(ml) (gui) (ml) (gm)
1.005 487 510 113 93 1.010 500 54 100 82 1.015 513 538 87 71
1.020 526 532 74 60
1.025 539 565 61 50
1.030 553 579 47 39
falling drop method of determining spe-cific gravity.
J.
Biol. Chem., 69:625, 1926.2. Banbour, H. G., and Hamilton, W. F. :
Fall-ing drop method for determining specific
gravity: clillical applications. J.A.M.A.,
88:91, 1927.
3. Fisher-Davidson : Modern Laboratory
Ap-pliances. Fisher Catalog, 1959, p. 580.
4. Kirk, P. L. : Quantitative Ultramicroanalysis.
New York, Wiley, 1950, pp. 294-299.
5. Peters,
J. J.,
and Van Slyke, D. D. :Quanti-tative Clinical Chemistry, Vol. 2. Meth-ods. Baltimore, Williams and Wilkins,
1956, pp. 941-958.
KRANKHEITEN DEll NEUGEBORENEN (Disease
of the Newborn), edited by Albrecht
Peiper, M.D. Leipzig, Germany, Veb
Georg Thieme, 1958, 131 pp.
A short compendium for students and
physi-cians interested in the treatment of disease of the newborn period coming from behind the
“Iron Curtain.” The book shows an extensive
knowledge of the “Free-World” medical litera-tune on such subjects as erythroblastosis fetalis,
cytomegalic inclusion disease, toxoplasmosis and other diseases of recent interest.
A chapter on infant mortality is extensive
and shows a similar decline of the death rate over the last decades as in the United States.
The over-all mortality during the first year of
life per 1,000 live-born in 1954 shows 49.6
deaths/1,000 in East Germany and 42.2
deaths/1,000 in West Germany. Infant
mor-tality in the United States amounted to 26.4
deaths/1,000 in 1955.
Of interest is a chapter on Listeniosis, a
zoon-osis transmitted to the pregnant mother
through direct contact with infected animals or
through ingestion of nonpasteunized milk. At
the University Clinic (Halle, Saxony) alone, 88 cases have been documented. Similar lange series have been reported from other centers
in Germany and Czechoslovakia. The causative
organism is a gram-positive rod, Listenia mono-cytogenes, belonging to the family of the con-ynebacteriaceae. The mother suffers from an
acute illness with fever and pyelitis resulting in
abortion or premature birth. In the newborn,
signs of fever, respiratory distress, and opistho-tonos occur shortly after birth. Roentgenogram
of the chest shows a diffuse pneumonitis. At
au-topsy, small granulomatous lesions are spread
over the liver, spleen, intestinal tract and lungs.
The organism can be cultured from blood, stool
and urine and is sensitive to penicillin and other
antibiotics. Serologic tests in the mother are
positive.
Otherwise, the book does not reveal any
