The salt content of the water can be measured very precisely using the conductivity method. Salinity can also be measured with a hand held refractometer. A refractometer measures the change of direction or bending of the light as it passes from air to water. Light moves slower in water than air. The more salt in the water, the slower the light moves. You can see the effect of light bending (refracting) as it passes from the water into the air by placing a pencil in a glass of water. The pencil appears to bend where it enters the water.
Red blood cells and haemoglobin. Oxygen is one of the substances transported with the assistance of red blood cells. The red blood cells contain a pigment called haemoglobin, each molecule of which binds four oxygen molecules.Oxyhaemoglobin forms.he curve shows that: 1  at relatively low oxygen concentrations there is uncombined haemoglobin in the blood and little or no oxyhaemoglobin, e.g. in body tissue. 2  at relatively high oxygen concentrations there is little or no uncombined haemoglobin in the blood; it is in the form of oxyhaemoglobin, e.g. in the lungs.
Red cells, or erythrocytes, are relatively large microscopic cells without nuclei. In this latter trait, they are similar to the primitive prokaryotic cells of bacteria. Red cells normally make up 40-50% of the total blood volume. They transport oxygen from the lungs to all of the living tissues of the body and carry away carbon dioxide. The red cells are produced continuously in our bone marrow from stem cells at a rate of about 2-3 million cells per second.