Ground Glass Stoppered Jars for Fluid Collections

Requirements for storage container

• The container must be made entirely of glass because it has a sufficiently long shelf life; fluid levels can easily be monitored; specimens can be initially examined in situ; and internal labels can be read through the glass.
• The glass must be toughened (borosilicate) for safety.
• The walls of the jar must be straight and parallel for safe handling.
• The jar must have an unrestricted neck.
• The lid must be individually ground to fit the jar and have a strong bar to assist opening.
• The jar must have a broad flat base.

Taper trials

Several old-style jars were used by the manufacturer for initial taper trials, and into these were ground custom-made stoppers with various gradients (Fig. 1).

Figure 1. Testing of the various taper gradients for the seal on the glass ground stopper.

The taper on the seal proved crucial.

1. An angle of 1:5 was too steep and a minor variation in the jar height would produce difficulties in getting an accurate, repeatable grinding suitable for mass production.
2. A ratio of 1:15 was too parallel and the lid proved difficult to rotate and consequently disengage from the jar.
3. An intermediate angle of 1:10 proved to be satisfactory for a good seal.

Lids

1. The most economical method of manufacture was for each jar to have an individually ground lid. The specification (Fig. 4). emphasized the need for extra thickness around the neck of the jar to ensure adequate strength after grinding.
   
   
   Figure 4. The factory specifications for production of ground glass stoppered jars
   
   
2. The bar on the lid initially proved to be too small and difficult to grip ( Fig. 2). A new stopper was designed with a much larger bar (Figs. 3, 5).

Figure 2. The first batch of ground glass stoppered jars ranging in size from 120mm to 500mm tall.

Figure 3. left, The prototype jar with the improved lid stands next to
                preproduction sample. The jar is 100mm in diameter 
                and 250mm in height.

Figure 5. The specifications for the stoppered lid improvements.

• Ground glass jars
  
  
  

The range of sizes was limited for reasons of economy. Two diameters give a good selection, 80mm and 100mm. These can be produced in four jar heights, 120mm for the former, and 150mm, 250mm and 500mm for the latter (Fig. 2). 

Consideration was given to producing glass cylinders for storing larger specimens because above 100mm diameter, ground glass jars are prohibitively expensive. These cylinders are made in three sizes, 300mm high with 250mm and 150mm diameters, and 450mm high with a 200mm diameter. The cylinders have a 25mm wide flange around the top and are sealed by a 5-6mm thick disc of plate glass.