A scattering photometer for measuring the light scattered by particles in a hydrosol at substantially 2.degree. and 90.degree. simultaneously. Light from a source is directed by a first optical system into a scattering cell containing the hydrosol under study. Light scattered at substantially 90.degree. to the incident beam is focused onto a first photoelectric detector to generate an electrical signal indicative of the amount of scattered light at substantially 90.degree.. Light scattered at substantially 2.degree. to the incident beam is directed through an annular aperture symmetrically located about the axis of the illuminating beam which is linearly transmitted undeviated through the hydrosol and focused onto a second photoelectric detector to generate an electrical signal indicative of the amount of light scattered at substantially 2.degree..

BACKGROUND OF THE INVENTION 
1. Field of the Invention: 
The present invention relates to light scattering photometers for making 
multiple measurements simultaneously and, more particularly, to apparatus 
permitting the simultaneous measurement of light at two different angles 
in a photometer. 
2. Description of the Prior Art: 
Inhomogeneity in the indices of refraction of particulates in natural 
waters leads to scattering of an incident beam of light, the intensity of 
the scattered light varying with its angular relationship to the optical 
axis of the incident beam. It has been found that particulates present in 
sea water having a high index of refraction, substantially 1.15 relative 
to water, characteristic of inorganic materials such as silica or calcium 
carbonate and organic skeletal material, tend to scatter light at large 
angles, greater than 80.degree.. On the other hand, particulates in sea 
water having a low index of refraction, 1.01 to 1.05 relative to water, 
characteristic of organic material, play a strong role in the scattering 
of light at smaller angles, 1.degree. to 10.degree.. These results suggest 
that a scattering photometer capable of simultaneously observing the light 
scattered at a small angle of scattering, 1.degree. to 10.degree., and at 
a large angle of scattering, greater than 80.degree., could distinguish 
between the low and high index particulate matter present in natural 
waters and industrial streams. 
Known prior art scattering photometers are incapable of simultaneous 
measurement of light scattered at both a small angle of scattering and a 
large angle of scattering. Additionally, they are incapable of continuous 
operation while a liquid suspension or hydrosol is being pumped through 
the scattering cell, as would be the case for example, if the photometer 
were operated aboard a ship underway. Furthermore, these instruments are 
large and bulky and incapable of considerable miniaturization. 
BRIEF SUMMARY OF THE INVENTION 
It is therefore one object of the present invention to provide a scattering 
photometer which is able to measure both small and large angle scatterings 
simultaneously. 
It is another object of the present invention to provide such a scattering 
photometer which is small, compact, and can be operated continuously while 
a sample stream of water flows through the scattering cell. 
It is yet another object of the present invention to provide such a 
scattering photometer which, with suitable calibration and use of 
appropriate formulas, can be used to determine the volume concentration of 
organic and inorganic, including organic skeletal, particulates present in 
a stream of water flowing through the scattering cell. 
The objects of the present invention are achieved by a photometer for 
measuring the light scattered by particles in a hydrosol at substantially 
2.degree. and substantially 90.degree. simultaneously. The photometer 
comprises a body having a passage for receiving the hydrosol, a light 
source, and first optical means for directing light of the source toward 
the hydrosol in the passage as an incident beam having an optical first 
axis. The photometer further includes a first photoelectric detector and a 
second optical means having an optical second axis at an angle of 
substantially 90.degree. relative to the first axis through their point of 
intersection which directs light of the beam scattered by the hydrosol 
onto the first photoelectric detector. A second photoelectric detector and 
third optical means are provided, the third optical means having an 
aperture and directing light of the beam scattered by the hydrosol onto 
the second photoelectric detector, the axis of the portion of the incident 
beam linearly transmitted by the hydrosol and the rays of the incident 
beam scattered through the aperture defining an angle of substantially 
2.degree.. The photometer further comprises a light trap for absorbing the 
light linearly transmitted by the hydrosol, and means in circuit with each 
of the photoelectric detectors for providing an indication of the amount 
of light directed toward each detector by the associated optical means. 
The foregoing, as well as other objects, features and advantages of the 
present invention will become more apparent from the following detailed 
description taken in conjunction with the appended drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to the drawings, wherein like reference numerals designate 
identical or corresponding parts, there is shown in FIG. 1 a diagram of a 
first embodiment of the 2.degree./90.degree. scattering photometer. 
The scattering cell 11 is a body having a passage containing the hydrosol 
under study. Light emitted by a laser light source 13 is directed by an 
optical system 15 as an incident beam having an optical axis intercepting 
the passage in the scattering cell 11. The optical system 15 comprises the 
pinhole spatial filters 17 and 19, the beam splitter 21, the calibrated 
neutral density filter 23 and the laser output monitoring detector 25. A 
chopper wheel 27 driven by a synchronous motor 29 is interposed between 
the light source 13 and the optical system 15 to interrupt periodically 
the emitted light. A light-source detector pair 31 is positioned to direct 
another beam of light through the chopper wheel 27 to provide a reference 
signal for use in the synchronous detection of the laser light scattered 
by the hydrosol passing through the scattering cell 11. The laser light 
beam emerging from the chopper wheel 27 passes through the pinhole spatial 
filter 17 onto the beam splitter 21. The pinholes 17 and 19 serve to 
prevent stray scattered light and multiply-reflected light from reaching 
the scattering cell 11. The beam splitter 21, an uncoated optical glass 
interposed between the pinhole spatial filter 17 and the calibrated 
neutral density filter 23 directs a small portion of the light from the 
source onto the laser output monitoring detector 25 while permitting most 
of the light to pass through the beam splitter 21 and then through the 
calibrated neutral density filter 23 into the spatial pinhole filter 19. 
The light emerging from the spatial pinhole filter 19 passes in the front 
window 33 of the scattering cell 11 into the hydrosol to be tested. The 
calibrated neutral density filter 23 permits reduction of the incident 
beam irradiance by an accurately known amount to prevent saturation of the 
photoelectric detectors used in the detection of the laser light scattered 
by the hydrosol. 
Although the above description of the first optical system is preferred, it 
should be understood that many other conventional optical devices may be 
used in order to direct the light beam into the hydrosol flowing through 
the passage in the scattering cell 11. 
The hydrosol will scatter light in all directions, but the intensity of the 
scattered light will vary with its angular relationship to the optical 
axis of the incident beam. A second optical system comprising a focusing 
lens 35 is arranged to receive light scattered through the window 37 in 
the side of the scattering cell 11 and directed on a photoelectric 
detector 39, preferably a silicon diode, which generates an electrical 
signal commensurate with the intensity of the scattered light received. 
The optical axis of the focusing lens 35 defines an angle of substantially 
90.degree. relative to the optical axis of the incident beam, and the 
focusing lens is spaced from the incident beam in accordance with the 
formula 
EQU 1/S.sub.1 + 1/S.sub.2 =1/f 
where S.sub.1 is the distance from the lens 35 to the incident beam, 
S.sub.2 is the distance from the lens 35 to the detector 39, and f is the 
focal length of the lens 35, thus, insuring that the scattering volume of 
light is focused at the proper magnification on detector 39. A third 
optical system 41 is arranged to receive light scattered through the 
window 43 in the rear of the scattering cell 11 and to direct it on a 
second photoelectric detector 45. The third optical system 41 comprises a 
radiant energy mask 47 spaced from the point of intersection in the 
direction of the axis of the incident beam away from the light source 13 
and having an annular aperture 49 for projecting a cone or portion thereof 
of the scattered light onto the focusing lens 51 for imaging at the second 
photoelectric detector 45, preferably a silicon diode. The spacing of 
radiant energy mask 47 and focusing lens 51 is arrived at in the same 
manner as the spacing of focusing lens 35. The light of the beam linearly 
transmitted by the hydrosol in the scattering cell 11 in the direction of 
the axis of the aperture 49 is largely absorbed in a light trap 53 located 
on or near the radiant energy mask 47. The light trap is a bent 
cone-shaped container having one open side and black internal walls. The 
annular aperture is symmetrically located about the axis of the portion of 
the laser beam linearly transmitted by the hydrosol, the axis and the rays 
of the incident beam scattered through the aperture defining an angle of 
substantially 2.degree.. The photoelectric detectors are connected in 
circuit with separate indicating devices 55 and 57, each equipped with a 
galvanomoter from which the amount of light received by the associated 
photoelectric detector can be read using synchronous detection techniques 
which are well known to those skilled in the art. 
A second embodiment of the 2.degree./90.degree. scattering photometer is 
illustrated in FIG. 2. It differs from the device described above by the 
removal of the chopper wheel 27 and light source detector pair 31 and by 
the substitution for the first optical system 15 of the microscope 
objective lens 59, the collimating lens 61, and the pinhole spatial filter 
63 for directing light of the source passing through the microscope 
objective lens onto the collimating lens, and thence to the hydrosol under 
study. In addition, the third optical system 41 has been replaced by the 
focusing lens 65, and the mask 67 at its focal plane having an annular 
aperture 69 for permitting a cone of the scattered light to be incident 
onto the second photoelectric detector 45, now disposed directly behind 
the mask. As before, light of the beam linearly transmitted by the 
scattering cell in the direction of the axis of the aperture is largely 
absorbed in a light trap 71, or, if desired, it may be transmitted through 
a hole located in the center of the detector 45 to a light trap located 
behind the detector 45. 
Supporting structure and other conventional elements have been omitted from 
FIGS. 1 and 2, and the elements illustrated will be recognized by those 
skilled in the art as representative of several types of elements that can 
be used. Thus, the laser 13 can be replaced by a small source of light, as 
for example, a General Electric No.1649 filament lamp and collimating 
lens, and the focusing lens 35 can be replaced by a baffled tube. 
FIG. 3 illustrates a horizontal cross sectional view of the scattering cell 
11. The passage 73 permits the hydrosol under study to pass through the 
scattering cell in the vertical direction. A stirring magnet 75 activated 
by the motor 77 and driving magnet 79 agitates the hydrosol. The front, 
rear and side windows, 33, 43 and 37 are provided to permit light to pass 
through the scattering cell 11 and are pressure fitted against the seals 
81, 83 and 85 by means of window adjustment screws 87, which also serve as 
a means for proper alignment of the windows with respect to the 
illuminating beam. 
In order to calibrate the 2.degree./90.degree. scattering meter, the 
calibration reference cells shown in horizontal cross section in FIGS. 4 
and 5 respectively are substituted for the scattering cell 11. In both 
cases, light from the laser 13 is incident on the center of a disc-shaped 
opal glass diffuser 89. A pinhole aperture 91 fits snugly against the 
diffuser to select a portion of the central bright spot of the diffuser 
having approximately uniform radiance. A retainer ring 93 maintains the 
diffuser and pinhole aperture in place. In the 90.degree. reference cell 
95 of FIG. 5 a mirror 97 is provided to reflect the laser beam onto the 
center of diffuser. The edges of the pinholes of the apertures are wafer 
thin to minimize edge effects. The pinholes approximately match the 
diameter of the laser beam. Thus, when the 2.degree. reference cell 99 is 
in place the lens 51 forms an image of the 2.degree. diffuser pinhole 
which is approximately the same size as the image of the scattering volume 
on the detector 45 when the scattering cell 11 is used. The diameter of 
the 2.degree. photoelectric detector 45 is chosen to be approximately 
10-20% larger than the images of the calibration diffuser pinhole and the 
scattering volume. When the 90.degree. reference cell 95 is in place, the 
lens forms an image on the 90.degree. photoelectric detector 39 of the 
illuminated portion of the scattering medium within the cell. This image 
has the shape of a long, thin rectangle. The 90.degree. detector diameter 
is approximately seven times the width of this image. When the scattering 
cell 11 is replaced by the 90.degree. reference cell 95, an out-of-focus 
image of the diffuser 89 and pinhole 91 falls on the detector 39. This 
arrangement spreads the light from the diffuser over a larger area of the 
detector than would be the case if the image were in focus and thereby 
minimizes errors due to nonuniformity of response over the detector area. 
In operation, the 2.degree./90.degree. scattering meter is first calibrated 
by substituting the calibration reference cells for the scattering cell 
and measuring the signal output of the 2.degree. detector with the 
2.degree. calibration reference cell in place, and the output of the 
90.degree. detector with the 90.degree. calibration reference cell in 
place. The calibration reference cells are then removed and the scattering 
cell is replaced in the scattering meter. The volume scattering functions 
in the 2.degree. and 90.degree. directions or the volume concentration of 
the scatterers can then be determined directly from the measured detector 
signals by use of appropriate formulas. 
Obviously, numerous additional modifications and variations of the present 
invention are possible in light of the above teachings. It is therefore to 
be understood that within the scope of the appended claims the invention 
may be practiced otherwise than as specifically described herein.