Novelty by exclusion

I was recently on holiday and found myself wandering through a greenhouse at the botanic gardens in Sheffield. I came across a liquid max/min thermometer hanging on a tree and this transported me back to a patent I drafted many years ago.  Max/min thermometers are often found in greenhouses, to enable a gardener to determine the maximum and minimum temperatures found in a greenhouse, in order to ensure that neither the maximum temperature  is too high, nor the minimum temperature too low.  Nowadays most max/min thermometers are of a digital type, but the patent I drafted was to a traditional max/min thermometer that employs a liquid which expands and contracts due to temperature changes. 

In case you are not familiar with a traditional max/min thermometer and how it works, I shall briefly explain. A traditional max/min thermometer is usually U-shaped with two arms filled with alcohol and mercury. One arm displays the maximum temperature and the other arm the minimum temperature. Within each arm there is a metal index which is moved in response to the expansion or contraction of the liquid within each arm and the metal indices come to rest at the respective maximum and minimum temperatures reached.

As mentioned above, traditional max/min thermometers included mercury. However, due to increasing environmental and health concerns, there was a desire to replace mercury within such max/min thermometers and I was approached by my client, as they had been developing alternatives to the use of mercury. My client had developed a number of liquids that could be used to replace mercury. However, I was concerned that by presenting a claim that defined chemically the liquids they had identified, it may be possible for a third-party to avoid infringing the claims of my client's patent, simply by substituting with an alternative liquid. 

Having considered what had previously been disclosed in the patent and scientific literature, it seemed to me that prior to my client identifying the problem of using mercury and providing possible solutions, no-one else had done so. Thus, I felt it was appropriate and commensurate with my client's contribution, to try and claim a liquid (i.e. not digital) max/min thermometer that was mercury free, rather than defining any specific alternatives to mercury in the broadest claim. I am pleased to say that the European patent office agreed that by stating the liquid was mercury free, this was considered novel and moreover inventive over what was know and described previously. As such I was able to obtain very broad claim language for my client and make it difficult for another manufacturer to come on to the market with liquid max/min thermometers that did not include mercury.

As mentioned above, I believe that most max/min thermometers now on the market are of a digital type, but I was pleased to see the one in Sheffield was a traditional liquid max/min thermometer and the memories this invoked.