The following points highlight the four main instruments that are used for collection of core samples. The Instruments are: 1. Hiller Borer 2. Russian Borer 3. Piston Sampler 4. Mackereth Sampler.
1. Hiller Borer (Fig.13.1):
In this instrument the filling of sediment is done by turning the apparatus anti-clockwise. Here outer, loose jacket with a projecting lip remains stationary and due to the turning of inner chamber, the longitudinal slits of jacket and chamber coincide.
The rotation of jacket is made by further anticlockwise turning and as a result the chamber fills with sediments. The chamber is then closed by turning the other way before pulling up.
The samples are taken out by opening the chamber. This instrument has certain disadvantages such as probability of surface contamination, cleaning problem, and difficulty to get intact core sample. But the modified version of Hiller borer (Thomas, 1964) overcomes such disadvantages. Here auger head is removable and the rotating inner chamber is lined with plastic or zinc to avoid surface contamination.
2. Russian Borer:
This sampler was devised by P.C. Jowsey in 1966 and is popularly known as “Russian borer”. This is an alternative instrument for sampling peats and well consolidated limnic sediments. Unlike Hiller borer, it has no auger head and after rotating the chamber, the core is fully exposed on the fin.
The core can easily be slid into a container and finally send to laboratory as uncontaminated intact core sample. The process of cleaning is easy involving wiping over of the fin surface. The disadvantage of this instrument is that it cannot be used for stiff sediments.
3. Piston Sampler (Fig.13.1):
Several piston samplers are used for well-decomposed, sloppy peats and lake sediments. Among these “Dachnowsky sampler” modified by Livingstone and others is found to be the best known sampler based on end-filling principle. It consists of a movable piston in an open-ended cylinder and a jacket. During collection the piston is held rigid and the cylinder is pushed into the deposit. The sample is withdrawn with the piston at the tip of the core.
4. Mackereth Sampler:
Mackereth (1958) designed a modified sampler, “Mackereth sampler” where the driving forces are a combination of vacuums and hydrostatic pressure. In this instrument depth of the entire sediment can be obtained in single underwater coring and the core is recovered under pressure.