Likewise, the invention deals with an oil-absorbing, granular substance of the kind changing colour, consistence and/or other natural properties when it comes into contact with oil and which, thus, is well suited as an indicator in said device.

In order to restrict the discharge of oily waste water into the sewer system, i.a. requirements have been introduced con- cerning the installation of oil-desorbers in petrol stations, workshops, industrial plants, etc. Even if a plant has in- stalled such an oil-desorber and, moreover, satisfactory operational and discharging routines associated with the use of such a desorber is maintained, it happens, nevertheless, that oily waste water is supplied to sewer system and envir- onment.

Hitherto, it has been difficult to detect the source of such undesired discharges of oil, and tracking of oil discharge sources represents laborious operations for municipal con- trol instances. In accordance with prior art technique, dis- charge may at best be found, and the volume of discharged oil has to be estimated.

The object of the invention has been to provide a device for pointing out the presence of petroleum and the like e.g. in waste water simply and rapidly.

The device comprises an encapsulated granular substance ex- hibiting such natural properties as changing colour and/or consistence when it comes into contact with petroleum-based liquids/hydrocarbons.

As one usable substance, e.g. styrene-copolymer can be used which is a white, solid granulate exhibiting varying grain sizes. This substance changes character - colour and con- sistence - when it comes into contact with hydrocarbones, i.e. in practice in the form of oily waste water. Hydrocar- bones become absorbed by styrene-copolymers and, thus, the hydrocarbones can not be washed out from the polymer. Con- sequently, a substance of this type is well fitted as an indicator in a device according to the invention.

The grained substance exhibiting such a general nature that it changes properties/condition when it comes into contact with petroleum-based liquids, is - according to the invention - encapsulated within a closable liquid-permeable cover, case, bag or the like which, already in this simple form, repre- sents a usable solution to the problem of detecting oil dis- charge and oil discharge source and, as such, may be posi- tioned downstream of said oil-desorber or another cleaning means for liquid polluted with oil.

In order to arrive at a less sensitive device to external influence of force, said liquid-permeable bag/cover or the like containing said granular substance, can be placed in a closable/openable rigid, perforated outer container accom- modating and protecting the bag/cover filled with substance granulate. This outer container may be equipped with an attaching means, e.g. an elongate fastener in the form of achain or the like and be positioned downstream of said purifying plant.

In the embodiment comprising internal, liquid-permeable bag and external perforated, rigid cylindrical protective con- tainer, the container may, in typical cases, have a length of about 20 centimetres and a diameter of about 6 centimetres.

At each control measurement, the external container is opened and its internal bag/cover is taken out and opened, where- after the originally grained substance is examined in order to ascertain possible change of colour and/or change of con- sistence. After use, the bag and its content is discharged, and the external container is provided with a new bag.

A device containing an indicator substance according to the invention will to a high degree simplify the work to locate the outlets where the waste water contains petroleum-based liquids. Thus, also the individual workshop or municipal in- stance may rapidly and efficiently take samples in order to control how various storage and treatment equipment for oil and similar substances functions.

The device according to the invention will also be usable in order to ascertain that discharge of hydrocarbon have not taken place downstream of oil-desorber or other purifying means for liquid polluted with oil.

During a period of 7 weeks, 37 devices containing an oil indicator substance according to the invention were posi- tioned downstream of 6 different oil-desorbers, distributed among 5 plants. In 4 of the 6 places for positioning, the changes in the substance nature and character showed oil in the waste water. In this test period of 7 weeks, it was established a clear connection between use of paraffin as a degreasing agent and positive deflections in the devices.

A non-restricting example of a device in accordance with the invention is further explained in the following, reference being made to the drawings, where: Figure 1 shows an exploded view in perspective of a device in accordance with the invention, a piece of cloth material being cut out in a cover-/bag-like inner container, in order to show that the cover/bag is filled with a grained, oil-absorbing substance and, thereafter, closed; Figure 2 shows the main components of the device in assembled condition.

Into an elongate, liquid-permeable cover/bag 10, which may have ends adapted to be pursed together, a granular, oil- absorbing substance 12 is filled. The substance 12 has a ne- glectable solubility in water, and may consist of styrene- co-polymer, which is a white, solid substance in the form of a granulate having varying particle sizes. A condition for the property of such a substance is that it is subjected to a change of state when it comes into contact with oil or other petroleum products.

In order to keep the granular substance 12 enclosed within the cover 10 intact and not disappear through damage on the cover/bag 10, the latter may, preferably, be placed in a rigid, perforated container 14.

The external perforated container 14 is, besides end pieces 14a and 14b, of which one 14a is fixed and the other 14b has the form of an end cover to be screwed or displaced into the open end portion, formed by a circle cylindrical body 14c having a large number of holes 16.

When controlling e.g. the oil-desorber after which the oil detecting device 10,12,14,16 according to the invention is coupled, the external, perforated container 14 is opened the cover 14b of which may, possibly, be sealed, and the bag/cover 10 with the substance particles 12 is taken out and opened, whereafter the granular substance 12 is examined with a view of, possibly, pointing out a change of state.

If the substance 12 has not been subjected to appreciable changes, the waste water is without oil, and the oil- desorber/purifying device functions satisfactorily.